The blinded method, which is commonly used in clinical medicine, pharmacology and psychology, aims to avoid the subjective bias by observers such as expectation. However, such method has largely been neglected in the studies of animal behavior. Recent reviews found that most studies, which blinded methods were needed, did not perform an experiment with blinding design. The effect size of such studies were significantly larger than which the blinded methods were used. Here we introduced the blinded methods and emphasized their role in the studies of animal behavior. We also illustrated the application of this method and provided suggestions for the studies of animal behavior in the future.