Abstract: Studies on the effects of different concentrations of triadimefon on cucumber seedlings growth and their resistance to chilling injury showed that 20～100 μmol·L^-1 triadimefon inhibited the shoot or root length of cucumber seedlings, and increased their root weight or root/ shoot ratio and chlorophyll content significantly.After at low temperature for 3 days, a higher chlorophyll content, lower membrane relative permeability and higher SODactivity were observed in the leaves of cucumber seedlings soaked with 10～50 μmol·L^-1 triadimefon.50 μmol· L^-1 triadimefon could retard the accumulation of MDA at low temperature stress.It was also observed that 50 μmol·L^-1 triadimefon enhanced the accumulation of praline at the first day of chilling treatment.However, higher concentrations(> 100 μmol ·L^-1) of triadimefon were unfavorable for cucumber seedlings to defense a-gainst low temperature.It was thus concluded that triadimefon protected the cucumber seedlings against low temperature.