Abstract: Objective To investigate the effects of creatine supplement on contractile properties of soleus (SOL) and extensor digitorum longus (EDL) in elder rat. Methods 20 male Sprague-Dawley rats were randomly divided into control group and creatine supplement group with 10 rats in each group. After 6 weeks, the content of creatine and phosphocreatine were detected by high performance liquid chromatography,and contractile properties were examined in SOL and EDL in vitro at 30 ℃. Results The content of creatine and phosphocreatine both in SOL and EDL were higher in the creatine supplement group than in the control group (P<0.05). In SOL, creatine supplements increased the maximum twitch tension (Pt), maximum titanic tension(P0), decreased time to maximum twitch tension (TPT), but only time from maximum twitch to half relaxation (TPR50) significantly decreased, compared with the control group. In EDL, creatine supplements significantly increased Pt, P0 and decreased TPT (P<0.05). But there was no significant difference in TPR50 between 2 groups (P>0.05). Creatine supplements significantly increased the fatigue resistance of the SOL and there was no significant effect on EDL. The force potentiation which occurred in EDL during the initial 20~30 s of the fatigue test significantly increased (P<0.05). Conclusion Creatine supplement is effective on the contractile properties of SOL and EDL in elder rats, but the effect is dependent on the fiber types.