This study was conducted in four separate experiments. In the first experiment, in January 2012, the freezing tolerance of seven olive cultivars, including Amphisis , Conservallia , Koroneiki , Manzanilla , Gorgan , Shengeh and Rashid , were compared with three approaches (electrolyte leakage, tetrazolium staining test, and maximum quantum yield of PSII photochemistry) after the cold treatment (temperature range 0 to -20 °C) and its correlation with some biochemical and physiological factors was investigated. In the second experiment, seasonal changes in in LT 50 , soluble carbohydrate, proline, malondialdehyde, DPPH scavenging capacity , total phenol, antioxidant enzymes activity (superoxide dismutase, catalase, peroxidase and ascorbate peroxidase) and protein content in the leaves of three olive cultivars ( Amphisis , Gorgan , and Manzanilla ) at six different dates: Nov., Dec., Jan., Feb., Apr., and Jul. and investigated their relationship with cold tolerance. The amount of saturated and unsaturated fatty acids and their ratio in two stages (Jun. and Jul .) was investigated. In the third experiment, the effect of foliar application of potassium sulfate on four rates (0, 0.5, 1 and 2%) on cold tolerance and some biochemical traits of olive cultivar Rashid were investigated as in the second experiment. In the fourth experiment, the effect of 24-epibrassinolide (0.1, 0.2 and 0.3 mg/l) and jasmonic acid (5, 25 and 50 mg/l) on the cold tolerance and some biochemical and physiological traits of olive cultivar Koroneiki were evaluated. In the first experiment, there was a high correlation between the cold tolerances of olive measured by all three methods. According to the LT 50 values, the tested cultivars could have been sorted out into three groups: freezing–tolerant cultivars ( Amphisis and Shengeh ( , intermediate-tolerant ( Consevallia and Gorgan ) and cold-sensitive cultivars ( Rashid , Koroneiki , and Manzanilla ). Higher concentration of soluble carbohydrates, proline, DPPH scavenging capacity and leaf tissue density and lower MDA content, stomatal density and RWC in leaf tissues were observed in cold tolerance cultivars, which confirms their protecting and stabilizing role to the cell membrane which makes these cultivars harder. In the second experiment, there was a significant difference between the olive cultivars in terms of freezing tolerance at each stage of sampling. The cold tolerance of cultivars increased during the cold acclimation stage and declined in the onset of deacclimation stage. In January, percentage of leaf dry matter, soluble carbohydrates, proline, total phenol content, antioxidant capacity and protein content, especially from the beginning of cold acclimation until full acclimation, in cold-tolerant Amphisis cultivar was more than the intermediate-tolerant Gorgan and the cold-sensitive Manzanilla cultivars. As a result, these compounds play an important role in increasing cold tolerance and can be used as indicators to screening the freezing tolerant olive cultivars. The highest of unsaturated/saturated fatty acids ratio in both months of Jun. and Jul. was detected in Amphisis frost-tolerant cultivar and the lowest was related to Manzanilla' s cold-sensitive. In the third experiment, foliar application of potassium sulfate, especially at a level of 2%, effectively improved frost tolerance in Rashid cultivar. There was a significant correlation between freezing tolerance and measured metabolites. The ability of Potassium in freezing tolerance improvement was found to be related to changes in metabolites such as accumulation of soluble sugars, proline, phenolic acids, antioxidant activity, and protein. The highest of unsaturated/saturated fatty acids ratio in both months of Jun. and Jul. was observed in 2% potassium sulfate treatment and the lowest was related to control treatment . In the fourth experiment, the foliar application of 24-epibrassinolide and methyl jasmonate significantly increased freezing tolerance in the Koroneiki cultivar. Key Words: Antioxidant enzymes, Freezing tolerance, Nutrition, Plant growth regulators, Osmoregulants, Olive, Cold acclimation, Electrolyte leakage.