Weekend ozone effect studied over a tropical rural and urban site in India shows higher ozone (O3) concentration on weekend compared to weekday. The weekend ozone effect was observed mostly during the summer and winter at the urban, and during summer season at the rural site. Decreased NOx emissions combined with VOC sensitivity on weekends appears to be the possible cause of the weekend ozone effect. The NOx concentration was low on weekend due to reduced commuter vehicular traffic emission. The results indicate nonlinear behavior in the chemistry of O3 production over the tropical region.