In animal behavior research, rat models of mental disorders (RMMDs) are developed to screen psychotropic drugs and to clarify the mechanism of mental disorders. Meanwhile, interaction between real rats is used to evaluate the RMMD. However, since rat-rat interaction is hard to control and quantify, we have adopted a bio-inspired robot to interact with real rats owing to its programmability and reconfigurability in testing different models. We have developed several rat-like robots before, however, these robots still can not fully satisfy the requirement of animal experiment. As an improvement, the newest generation rat-like robot called WR-5 is developed. WR-5 can perform mounting and grooming actions naturally as live mature rat owing to adopted differential gear in its waist. Preliminary SIT between WR-5 and mature rats have been conducted strictly following psychological rules. Experimental results show that rats are more active and have fewer frequencies of grooming and rearing actions when WR-5 performs mounting action periodically. The rat-like robot is therefore able to make the anxiety level of rats high by means of performing mounting action.