INTRODUCTION: Social play behavior is crucial for acquiring social skills and the development of normal socioaffective responses. The repertoire of social play in rats changes throughout the life, peaking during the juvenile period and falling off around adolescence. The most characteristic postures in social plays of rodents are pinning and pouncing. In addition to playful activities during social play, rats also engage in non-playful behaviors including social exploration. The lack of ability to engage in social play with conspecifics is the main indicator of neuropsychiatric disorders like autism. There is strong evidence suggesting that maternal infection during pregnancy is correlated with increased risk of developing autism spectrum disorder (ASD) in the child. To model maternal immune activation, polyinosinic: polycytidylic acid (poly(I:C)) is used to induce inflammatory response in the maternal-placental-fetal axis. The resulting inflammation leads to perturbation of the brain development of pups and consequently may lead to development of the symptoms of autism. AIM(S): We performed the Social Play Test to study changes in social play behavior of rats in an ASD model induced by prenatal exposure to poly(I:C). METHOD(S): Pregnant Sprague-Dawley rat dams received a single intraperitoneal injection of poly(I:C) (5 mg/kg) or vehicle at gestational day 15. The 30 – 35 days-old rats were then tested using the Social Play Test. RESULTS: Rats that were prenatally exposed to poly(I:C) demonstrated a significant decrease in a number of episodes of pinning compared to the vehicle-treat ed controls. We also observed significantly diminished time of social exploration in the offspring of poly(I:C) treated females. CONCLUSIONS: The present study demonstrated that prenatal exposure to poly(I:C) results in social deficits in juvenile rats. Measures of social play behaviours in rats could be useful for quantifying abnormal levels of sociability associated with autism. FINANCIAL SUPPORT: Supported by NSC grant: 2016/23/B/NZ7/01131.