Non-autistic adults often hold explicit and implicit biases toward autism that contribute to personal and professional challenges for autistic people. Although previous research indicates that non-autistic adults with higher autism knowledge and familiarity express more inclusionary attitudes, it remains unclear whether training programs designed to promote autism acceptance and understanding affect subsequent implicit and explicit biases toward autism. In this study, non-autistic adults (N = 238) completed an autism acceptance training featuring factual information and engaging first-person narratives, a general mental health training not mentioning autism, or a no-training control, then responded to surveys assessing their autism knowledge, stigma, and impressions of autistic adults, and completed a novel implicit association task about autism. Non-autistic adults in the autism acceptance training condition reported more positive impressions of autistic adults, demonstrated fewer misconceptions and lower stigma about autism, endorsed higher expectations of autistic abilities, and expressed greater social interest in hypothetical and real autistic people. However, training had no effect on implicit biases, with non-autistic adults associating autism-related labels with unpleasant personal attributes regardless of training condition. These findings suggest that the autism acceptance training program in this study, designed to increase autism knowledge and familiarity among non-autistic people, holds promise for reducing explicit but not implicit biases toward autism.