Fitspiration is a popular social media trend that aims to inspire individuals to improve their health and fitness through diet and exercise. However, viewing fitspiration content on Instagram has been identified as a contributor to negative body image, especially for young women. With the growing popularity of the video sharing platform TikTok and concerns over its content, the present study aimed to experimentally examine the effect of exposure to fitspiration TikTok videos on young women's body dissatisfaction, appearance comparison and mood. The roles of state appearance comparison as a mediator and trait fit ideal internalisation as a moderator were also considered. Young women (18-25, N = 120) from Australia were randomly allocated to view a set of fitspiration videos or a set of art control videos from TikTok. Results indicated that exposure to fitspiration TikTok videos increased state appearance comparison and state negative mood relative to art TikTok videos but did not directly increase state body dissatisfaction. State appearance comparison significantly mediated the effect of TikTok videos on body dissatisfaction and mood, however, there was no moderating effect of trait fit ideal internalisation. These findings highlight the importance of state appearance comparison in relation to viewing fitspiration content on TikTok.