In this research work, the first, calcium-amino chelates were synthesized and characterizd at the Soilless Research Centre of Isfahan University of Technology. Then, the efficacy of foliar spray of synthesized Ca-amino chelates in comparison with mineral Ca-salts on greenhouse cucumber was evaluated in a greenhouse at Khalajestan region, Dastjerd city, Qom province. Treatments included three amino acids i.e., lysine (Lys), methionine (Meth), and threonine (Thr) and their chelates with Ca i.e., [Ca(Lys) 2 ], [Ca(Meth) 2 ], and [Ca(Thr) 2 ]. All treatments were sprayed at a similar concentration of 0.5%. A free amino acid and free Ca treatment was also considered as the control. The experiment was carried out in a randomized complete block design in triplicates. Mature leaves and fruit of cucumber plants were sampled at two periods and plant yield, concentration of nutrients, and certain quality attributes of fruit were measured. Results obtained showed that the effect of foliar spray of synthesized Ca-amino chelates is associated with both amino acids and Ca and their interaction, so that the individual effects of amino acids and Ca observed at the amino acid and mineral Ca salts treatments were less effective than Ca-amino chelates. Foliar spray of [Ca(Meth) 2 ] was more effective than the other treatments in improving number and fruit yield of cucumber while the effect of [Ca(Lys) 2 ] on fruit quality attributes of cucumber was greater than the other amino chelates. The effect of [Ca(Meth) 2 ] and [Ca(Thr) 2 ] on fruit firmness was similar to [Ca(NO 3 ) 2 ] and [CaCl 2 ]. But [Ca(Lys) 2 ] had much greater effect on fruit firmness compared to the other Ca treatments. Application of free amino acids except threonine (Thr) had no significant effect on fruit firmness. Therefore, it seems that the main reason for variation of used amino chelates in improving fruit firmness is their differences in the ability of uptake or translocation of Ca in plant. Lysine (Lys) and threonine (Thr) and their chelates with Ca and [Ca(NO 3 ) 2 ] resulted in significant increase of soluble sugar concentration of cucumber fruit. This result indicates the effect of N in these treatments on fruit soluble sugar concentration. Ca-amino chelates resulted in significant increase of leaf and fruit Ca concentration and their effect was higher than the mineral Ca-salts. Application of Ca-amino chelates had greater effect on increasing total N content of fruit in comparison with the amino acid and even [Ca(NO 3 ) 2 ] treatments. According to the results obtained, application of synthesized amino chelates particularly [Ca(Meth) 2 ] and [Ca(Lys) 2 ] is recommended as effective source of Ca for greenhouse cucumber. Keywords: Lysine, Methionine, Threonine, Calcium chloride, Calcium nitrate, Fruit yield, Quality attributes, Fruit firmness