AbstractMale threespine sticklebacks (Gasterosteus aculeatus) prefer to court the more gravid of a pair of dummy females (Rowland1982, 1989). In this study, males were trained to modify their courtship preferences. Males were given two pre‐punishment preference trials during which two dummy females—one approximating a normally gravid female and the other, a supergravid female, possessing an abnormally large abdomen — were simultaneously presented to males. After pre‐punishment trials, males were subjected to one of two punishment procedures: punishment with weak electric shock (Experiment I) or punishment by the removal of females to simulate female retreat (Experiment II). During punishment trials, males were punished each time they courted the supergravid dummy. Control males were subjected to identical trials, but were not punished for courting the supergravid dummy. Post‐punishment preference trials were given to all males (Experiments I and II). The results of Experiments I and II were similar. Punished and control males did not differ in their courtship preferences in pre‐punishment trials; they preferred to court the supergravid dummy. Punished males, however, spent a significantly lower proportion of time visiting and directed a smaller proportion of zigzags (a courtship display) toward the supergravid dummy than did control males during punishment training (Experiment I) and post‐punishment preference trials (Experiments I and II). These results suggest that courtship preferences of male threespine sticklebacks can be modified through learning. Such a mechanism could be important for adaptive mate choice under natural conditions.