Research on the impact of ozone (O3) on fecundability has been inconclusive, lacking evidence examining the lagged pattern of ozone exposure and temperature modification. Current studies have predominantly been conducted in North America and Europe, leaving a gap in research from the Asian population. This population-based prospective cohort study involved 594,110 couples in Yunnan Province, China, enrolled in the National Free Preconception Health Examination Project. We calculated time-varying cycle-specific O3 concentration across 1-12 menstrual cycles before conception, according to each female's menstrual cycle length and residential addresses. Time to pregnancy was used as an outcome indicator. A discrete-time Cox regression model integrated with a distributed lag model (DLM) was employed for analysis. We observed that O3 exposure was negatively associated with fecundability, with the effect diminishing over time relative to conception. The first menstrual cycle before conception appeared most sensitive to O3 exposure, showing a 6.2 % decrease (HR: 0.938; 95 % CI: 0.936 to 0.941) in fecundability per one IQR increase of O3. Combined exposure to O3 and ambient temperature may exert a synergistic effect. The modifying effect of temperature was most pronounced in the first cycle before conception, with HRs of 0.891 (95 % CI: 0.886 to 0.895), 0.859 (95 % CI: 0.853 to 0.865), and 0.833 (95 % CI: 0.826 to 0.840) under low-, median-, and high-temperature conditions, respectively. Targeted policy interventions are needed to mitigate the dual impact of air pollution and rising temperatures.Copyright © 2025. Published by Elsevier Ltd.