This study investigated the relationships among leader–member exchange (LMX), perceived job security, and employee performance. Drawing on the job demands–resources model and conservation of resources theory, we expected both LMX and perceived job security would affect employee altruism and work performance in a positive manner. In addition, LMX and perceived job security were expected to interact to predict the two outcome variables. The hypotheses were tested with a sample of 184 employees in a state-owned enterprise in China. Our results showed that LMX, but not perceived job security, was positively related to employee altruism and work performance. Additionally, the effect of LMX on altruism was stronger for employees perceiving less job security. The findings indicated that LMX as a job resource becomes more impactful to altruistic performance when employees feel less secure at work.