The decrease in social interaction is found in various psychiatric diseases including schizophrenia, depressive disorder and autistic spectrum disorders. One of the reasons of this phenomenon can be attributable to social anhedonia -- difficulty for feeling of positive emotions by social interaction. We have demonstrated that place preference is caused by social interaction in rodents, and suggested that this method can be suitable for analysing social anhedonia. In this study, we have observed the effect of conditioned-place preference by social reward (SCPP) among 3,5,8, 12 weeks of age in order to elucidate the development of social hedonic emotions as developmental amelioration of symptoms were observed in autism. Male and female Wistar rats were used at ages indicated above. SCPP was conducted in three chamber system composed of right and left chambers (25 x 40 x 40 cm) that had a wall of white background with dots and black background with white lines, respectively, while middle chamber (15 x 40 x 40 cm) has separated by transparent walls from the other chambers. Acclimatization to chambers and 10-min pretest for measuring preferece of chambers was done at day 1, followed by 2-day resting period. From day 3 to 6, rats were introduced to preferred chamber at day 1 alone for 10 min and then to not-preferred chamber at pretest with a same-sex conspesific for 10 min. The preference of chambers were measured again at day 7. All behaviors were analyzed by Any-maze software (Stoelting co., IL, USA). The effect of SCPP was largest at 3 weeks of age and reduced with development. The difference in the stay-time in preferred and non-preffered chamber was significant at 3, 5, 12 weeks old, while three-way analysis of variance showed significant interaction between age and the stay-time change. There were no effects of sex in SCPP, although total distance travelled in chambers and total number entries in chambers were reduced with development in male. There results has raised the possibility that social reward become weak with development, although we could not deny the possible influence of developmental changes in the efficiencies of conditioning and anxiety which affects SCPP.