Genistein (Ge) and daidzein (Di), the active isoflavones primarily found in soybean, have various beneficial health effects. The present study aims to investigate the effects of these isoflavones on tight junction (TJ) barrier integrity in immortalized endometrial epithelial cells (IMM). Expressions of the TJ integrity markers, zona occludens‐1 (ZO‐1) and claudins (cldn)‐1, ‐3, ‐4, ‐7 and ‐8 were analyzed by quantitative reverse transcription and real‐time polymerase chain reaction (RT‐PCR) and transepithelial electrical resistance (TER) by voltohmmeter. Treatment with Ge (10 nM or 1 μM) for 48 h increased the TER, and this was correlated with the mRNA expression of cldn‐3 and/or ZO‐1. However, low dose of Ge (0.1 nM) decreased both the TER and the expression of cldn‐3 and/or ZO‐1. Di did not alter the expression of the TJ proteins. Our results suggest that genistein increases barrier function possibly via the expression of cldn‐3 and ZO‐1. This represents an important protective role of genistein against endometrial barrier disturbance.Grant Funding Source: Chulalongkorn University Research Fund and Srinakharinwirot University Research Fund