Abstract: Bitterlings are a group of small fishes in the family Cyprinidae with complicated reproductive behavior. In laboratory, they can be easily manipulated to testsome hypotheses of reproductive behavior. In the present study, we used the rose bitterling Rhodeus ocellatus as model. To understand the general rule of sexual selection in the rose bitterling and test some sexual selection hypotheses, we selected females and males with different body sizes. Meanwhile, we also examined the egg counts of females and spatial learning and memory abilities of males. The sexual selection of male showed that male significantly prefer larger females than smaller ones; both selective frequency and staying time of males to females were positively related to some characters displayed by females, such as standard length, body depth, length of ovipositor, etc. Based on the hypotheses of immediate benefits for males, the reason that males preferred to choose larger females to mate can be explained by the facts that larger females have longer ovipositor and more matured eggs, therefore high fecundity. Similarly, females also significantly prefer to choose larger males than smaller ones; both selective frequency and staying time of females to males were positively related to standard length and body depth; larger males were better in spatial learning and memory than smaller ones, which made them have stronger ability in monopolizing good mussels in reproduction. Subsequently, based on the hypotheses of immediate benefits for females, choosing larger males will improve the survival rate of their descendants since larger males can find and occupy good mussels easily and quickly.