<p>With rapid advances in technology, marketers are eager to adopt innovative promotion tools to give consumers a detailed understanding of products. Augmented reality (AR) and live streaming are emerging technologies that retailers are focusing on, but it is unclear how they will affect consumers and what the difference is. Based on the functional mechanisms of online product presentations, we examined how AR and live streaming affect online consumers’ product quality and fit uncertainty, and the differences in their influence mechanism. A between-subject experiment (<i>N</i> = 553) was conducted. The findings show that (1) AR, live streaming, and AR + live streaming all significantly enhance interactivity and vividness. However, the three presentation modes differ in their paths of impact, and their combined use is not superior to the individual use; (2) the sequence of interactivity/vividness and spatial presence/social presence mediates the relationship between AR or live streaming and product uncertainty; and (3) product type moderates the relationship between product presentation mode and product uncertainty. This study reveals the influence mechanisms and boundary conditions of AR and live streaming on product uncertainty, providing insights into how online retailing can effectively utilize these two technologies.</p>