The study on the effects of foliar spraying 20 mmol x L(-1) of CaCl2, Ca (NO3)2 and CaAc2 on the freezing resistance of satsuma mandarin (Citrus unshiu Marc. cv. Guoqing No. 1) showed that after treated with these Ca salts, the leaves of test plant had a lower half lethal temperature (LT50) than the control (sprayed with distilled water). The LT50 after treated with CaCl2 was 0.54 degrees C lower, whereas that after treated with CaAc2 and Ca (NO3)2 was 1.34 degrees C and 1.35 degrees C lower, respectively, implying that the latter two Ca salts were more effective in enhancing the freezing resistance of satsuma mandarin. Moreover, foliar spraying Ca salts increased the superoxidase (SOD) and peroxidase (POD) activities and the contents of soluble proteins, soluble sugars and praline in leaves, and decreased the leaf MDA content.