<p>Objectives　Few studies have focused on the relationship between smoking habits and occupation in Japan. This study aimed to examine the changes in smoking prevalence by occupation, specifically those occupations defined in the Japan Standard Occupational Classification (JSOC).</p><p>Methods　We analyzed data from the Comprehensive Survey of Living Conditions, a large nationally representative survey conducted in Japan every three years, between 2001 and 2016. Survey participants were asked whether they (1) “never smoked,” (2) “smoked daily,” (3) “smoked occasionally but not every day,” or (4) “used to smoke daily (before, at least one month).” Participants who answered (2) “smoked daily” or (3) “smoked occasionally but not every day” were considered “current smokers.” Age-standardized smoking prevalence was computed based on the JSOC (10 categories: administrative and managerial; professional; clerical; sales; services; security; agriculture, forestry, and fishing; transport; manufacturing, construction, mining, carrying, cleaning, and packaging; and unemployment). The analyses were restricted to workers and unemployed men and women aged 25 to 64 years old.</p><p>Results　Between 2001 and 2016, the smoking prevalence (of the entire population aged 25 to 64 years old) decreased from 56.0% (95% confidence interval [95% CI]: 55.8-56.3%) to 38.4% (95% CI: 38.1-38.6%) among men, and from 17.0% (95% CI 16.8-17.2%) to 13.0% (95% CI 12.8-13.1%) among women. In 2016, the smoking prevalence for clerical (the lowest smoking prevalence) and transport workers (the highest smoking prevalence) was 27.9% (95% CI: 27.0-28.8%) and 48.3% (95% CI: 46.8-49.7%), respectively, for men, and 9.4% (95% CI: 9.0-9.7%), and 38.5% (95% CI: 32.6-44.5%), respectively, for women. Between 2001 and 2016, the smoking prevalence for men decreased for all occupations, whereas for women, the smoking prevalence decreased for all occupations except for security and for transport workers. The largest reduction rate of smoking prevalence between 2001 and 2016 for men and for women was observed in clerical workers (−21.0%) and sales workers (−7.2%), respectively. We also found that clerical workers had the lowest smoking prevalence across the 5-year age categories for both sexes, especially the younger age, which resulted in the largest differences in smoking prevalence by occupation among men aged 30 to 34 years old.</p><p>Conclusion　We confirmed that, between 2001 and 2016, the lowest and highest smoking prevalence for both sexes is found among clerical workers and among transport workers, respectively. Although smoking prevalence has declined among working-aged men and women between 2001 and 2016, large differences by occupations consistently exist in Japan. It is necessary to take measures against smoking habits in consideration of their social backgrounds and work environments.</p>