Abstract: Seed of cucumber (cucumis satiwus L, Var. Jin Yan No.4) were germinated on filter paper saturated with distilled water at (25+1)C in dark or in light for five days. The excised cotyledons were in Ti-chelator solution. The fresh weight, contents of the carotenoid, chlorophyll, RNA and DNA of cotyledons were determined. The results showed that there were significant promotion in exhancing the expansion of cotyledons, the accumulation of carotenoid, the synthesis of chlorophyll, and increase of nucleic acid. The fresh weight and content of nucleic acid of excised cucumber cotyledons treated by Ti-chelator in light was greater than in dark. The effect of 2ug/mL Ti-chelator on DNA, RNA contents was a little bigger than 4ug/mL Ti-chelator, and the effect of Ti-chelator on DNA synthesis in light was great than in dark.