A pulse-chase labeling of $^{15}N$ on winter rye (Scale cereale) and forage rape (Brassica napus) grown at $15^{circ}C$ and $25^{circ}C$ was carried out to determine the effects of low temperature on the uptake exogenous N and the remobilization of endogenous N. The growth rate of leaves and roots depressed at $5^{circ}C$. AAer 9 days at $5^{circ}C$, nitrogen content of leaves decreased to 20% on the average while that of roots increased to 12% compared with the plants grown at $25^{circ}C$. Total content of $NO_3$- uptake 60m medium was 23.0 and 43.5 mg Nlplant, respectively, for winter rye and forage rape grown at $5^{circ}C$ during 9 days. These values were corresponded to 59.3 and 26.1% lower uptake than those of $25^{circ}C$. A large part of 1 5 ~ was distributed into leaves throughout time course in both of two species. The content of $^{15}N$ in leaves of winter rye at day 6 increased to 166 and 296 $mu^{15}$N/plant compared with the initial value (day 0) in the plants grown at $5^{circ}C$and $25^{circ}C$ , corresponding to 90 and 163 $mu$g N of remobilization h m roots into leaves during the fist 6 days. From 7 to 9 days, 75 and 52 $mu$gN of outflow 6om leaves were occurred at $5^{circ}C$ and $25^{circ}C$. However, little remobilization of endogenous N was estimated in forage rape throughout the entire time course regardless of temperature treatment. Comparing two species studied, winter rye was much sensitively influenced by low temperature on the uptake of exogenous N and the remobilization of endogenous N.