Autism spectrum disorder (ASD) is a lifelong neurodevelopmental disorder characterized by early-onset impairments in social communication, repetitive behaviors and stereotypies. The present study was designed to investigate the developmental alteration of social behavior in rat model of autism induced by valproic acid (VPA). Experiments were carried out on prenatally VPA-treated and control (saline treated) rats at two different ages: adolescent (postnatal day 30) and young-adult (3 months-old) male rats. Sociability was evaluated in a three-chamber apparatus. The results showed that groups of both ages spent more time in the compartment with an unfamiliar rat compared to an empty wire cage and spent more time sniffing the wire cage with rat than the empty wire cage. At this stage, the VPA treated group showed the same interest in social contacts as the control group. We also evaluated the social behavior by measuring sniffing time to either wire cage with familiar or unfamiliar rat. The VPA treated young-adult rats showed a significantly lower social approach than the control rats: control group spent more time sniffing the wire cage with unfamiliar rat than the cage with familiar rat. The preference for unfamiliar over familiar rat in adolescent VPA treated rats was not statistically significant. The identification of short-term and long-term behavioral characteristics in prenatally VPA treated adolescent and young-adult rats enhance our understanding of autism and to gain further insight into the developmental alteration of behavior in ASD.Supported by the funding from the SRNSFG: Grant # - YS-22-3231