For reducing planting distance in greenhouse grown watermelon(Citrullus vulgaris S.) this experiment was carried out to study the effect of DIF on stem elongation and growth. Day temperatures ranged from $25^{circ}C$ to 35$^{circ}C$ : night temperatures ranged from $25^{circ}C$ to 35$^{circ}C$ at 5$^{circ}C$ interval. Stem elongation, leaf size, dry weight and flowering were influence by day and night temperatures. Stem elongation and length of internode decrease with increasing night temperature at same day temperature. The optimums for number of leaves categories was with day at 35$^{circ}C$, and flower production was the lowest at $25^{circ}C$. Total leaf area meter was maximized at 35/30(DT/NT), but for size pet one leave was the largest 25/25(DT/NT). Responses of leaf size per leaves were similar to that of internode length, with maximum day and night at $25^{circ}C$. Total plant dry weight was the highest 35/30 (DT/NT) and minimum occurring at 25/30(DT/NT). The shoot/root ratios of dry weight Increased with day temperature up to 3$0^{circ}C$ and were the highest with night at $25^{circ}C$. Chlorophyll contents decreased with decreasing day and night temperature.