Abstract Smoking is the strongest established risk factor for bladder cancer. Former smokers have a lower risk of bladder cancer compared with current smokers, but findings on the dose–response relationship between years after quitting and the risk of bladder cancer are inconsistent. A total of 143,279 postmenopausal women from the Women's Health Initiative Study were included. Cox proportional hazards regression models were applied for estimating age- and multivariable-adjusted HRs and their 95% confidence intervals (CI). There were 870 bladder cancer cases identified over an average of 14.8 years of follow-up. After adjusting for pack-years of smoking, bladder cancer risk among former smokers declined by 25% within the first 10 years of cessation and continued to decrease as cessation time increased but remained higher than never smokers after 30 years of quitting (HR, 1.92; 95% CI, 1.43–2.58). Smokers who quit smoking had a lower risk of bladder cancer compared with current smokers (HR, 0.61; 95% CI, 0.40–0.94). We conclude that among postmenopausal women, there is a significant reduction in the risk of bladder cancer after quitting smoking. In addition to primary prevention, smoking cessation is critical to prevent the incidence of bladder cancer in older women.