Objective: To investigate the effect of microRNA let-7a on OPN expression in a mouse model of allergic rhinitis. Methods: Thirty-two mature female C57BL/6 mice were randomly divided into four groups, with eight mice in each group: microRNA let-7a, microRNA control, OVA and phosphate-buffered saline groups. The microRNA let-7a, microRNA control and OVA groups were sensitised with OVA to establish a mouse model of allergic rhinitis. Nose-scratching events were counted. Nasal mucosa was used to evaluate histological changes of goblet cell hyperplasia. Interleukins 5 and 13 were detected. Interferon- levels in the nasal lavage fluid were assayed with enzyme-linked immunosorbent assay. OPN expression was estimated with polymerase chain reaction. Results: Compared with microRNA control mice, microRNA let-7a treated mice had a significantly increased number of nose-scratching events, nasal mucosal eosinophilia and goblet cell hyperplasia (p < 0.05), and significantly higher interleukins 5 and 13 in nasal mucosa (p < 0.05), but there was no significant difference in interferon- (p > 0.05). In addition, microRNA let-7a treated mice had significantly enhanced OPN expression in nasal mucosa (p < 0.05). Conclusion: MicroRNA let-7a can promote allergic rhinitis development partly by regulating OPN expression.