Working memory has been considered an active buffer for processing perceptual representations in a progressive manner, integrating information involuntarily to form structured mental representations. The automatic integration of objects’ physical features in working memory has been well documented, although its social aspect remains unknown. The current study examines whether working memory would automatically process social information, that is, extract social information from memory content to form a higher-level social representation. Through four experiments, we demonstrate that participants could spontaneously infer personality traits when required to hold the social information implying others’ traits in working memory, without the explicit goal of trait inference or awareness of the inference processes. Results show that participants mistook the memorized words for inferred trait words; such “errors” were then accumulated and amplified when the information was transmitted from person to person, during which the social information was briefly stored in working memory and reproduced after a short time. These findings indicate that working memory may automatically integrate social information into hierarchically structured mental representations.