Purpose: Against the background of industrialisation and modernisation of agriculture, food production issues and environmental hazards have become more and more obvious and consumers are increasingly concerned about food safety and health, which is strengthening demand for organic food. E-commerce provides a new channel for sales. Research on consumer trust in online organic food sales is the basis of network marketing. The paper aims to discuss these issues. Design/methodology/approach: A laboratory experiment was used to empirically test the effects of media richness on consumers’ trust and the moderating effect of online review length. A 2×2 factorial design (i.e. two types of online product presentation formats (between-subject)×two levels of online review lengths (between-subject)) was used. Findings: Media richness has a significant positive effect on consumers’ trust and that this effect is moderated by online review length. Meanwhile, perceived risk conveys the interaction effect of the media richness of online product presentation and online review length to trust. Practical implications: E-commerce websites should aim to promote organic food by using a variety of online product presentation formats and by presenting high quality online reviews in order to reduce consumers’ perceived risk and improve their degree of trust when buying online. Originality/value: This paper provides a new insight into consumers’ attitude of buying organic food online. The results of the research could provide proposals for promoting organic food sales online. © 2017, © Emerald Publishing Limited.