The almond seed wasp, Eurytomaamygali , is a key pest of almond in Iran that can destroy, in some cases, up to 90% of the almond production. Because of this pest importance and the lack of adequate information on its overwintering strategies and its phenology in Isfahan, this study was carried out to investigate the phenology and diapause physiology of the almond seed wasp. For this purpose, changes in total sugar, glycogen, protein, lipid, alcohol sugars, supercooling point and cold hardiness of the pest were measuredmonthly in the overwintering larvae (September 2014–march 2015) and larvae with prolonged diapause(August and September 2015). The total sugar increased with decreasing temperature andreached the highest level(22.63±1.5 mg/gbody weight)in the coldest month (January). Alcohol sugars, trehalose and glucose, were also increased in proportion to the increase in total sugar and reached to the highest level in January (16±0.5, 7.2±0.53 mg/gbody weight,respectively).With decreasing temperature in January,glycogen content was decreased and reached tothe lowest level (28.11±1.6 mg/gbody weight). The maximum amount of protein (23.33±3.54 mg/gbody weight) was observed in February. Lipid content was increased in winter and the highest amount was observed in March (23.76±1.27mg/g body weight).Biochemical changes were also measured in larvae with prolonged diapause in August and September. Sugar, alcohol sugar, lipid and glycogen concentrations were decreased but protein content did not show significant differences. Supercooling point of the overwintering larvae was almost fixed from October to January around -23 °C, but in February increased to -18.6°C. Proportional to the increase in supercooling point, cold tolerance was decreased, so that the survival rate at -20°C in March reduced to 73.3%from 100%. The supercooling point and cold hardiness of larvae with prolonged diapauses showed no difference to the overwintering larvae (October to February). Time required for the death of 50% of the larvae (LT 50 ) at a temperature of -15 ?C were measured in October, November and December.The LT 50 of the larvae was increased from November to October. Based on the results, the breakdown of glycogen to sugar could have increased the cold tolerance of the pest. Thus, can survivethe successive winter frosts with low mortality.The incidence of prolonged diapauses in the Baghbahadoran region in 2015 was estimated 30%.The minimum temperature threshold of the pest was estimated 7.5 °C and constant temperature for pupal development in the laboratory conditions was 231.08±2.95 degree-days. Phenological study in Baghbahadoran weather conditions showed that termination of pest pupation occured on 30/3/2015(by about 139degree-days).Peak of adult emergence occurred on 25/4/2015(by about358degree-days). The peak of the egg laying was observed in1/5/2015(by 313.5 degree-days). Suitable fruit size for egg laying was about 1.5×2.5 - 2.4×3.5.The obtained information shows that this species could tolerate the district winter cold and have been adapted to the weather conditions. Keywords : Eurytomaamygdali, Diapause, Coldhardiness, phenology, temperature threshold.