Epidemiological studies have explored the relationship between work stress and the risk of cancer, but it remains unclear on whether work stress could increase the risk of cancer, or by other factors such as smoking and physical activity. Our study aimed to investigate the association between work stress and the risk of cancer and in relation to major potential confounding and modifying factors. We systematically searched three electronic databases, hand-searched references and citations of retrieved articles, and consulted experts to identify studies on assessing the association between work stress and the risk of cancer. The relative risks (RRs) of cancer associated with work stress were estimated using a random-effects model, and stratified by exposure measurement, study design, gender, study location, cancer site, smoking, drinking, body mass index, and physical activity. A total of 281,290 participants were included in this analysis. The significant association between work stress and the risk of colorectal (RR = 1.36; 95%CI: 1.16-1.59), lung (RR = 1.24; 95%CI: 1.02-1.49), and esophagus (RR = 2.12; 95%CI: 1.30-3.47) cancers were found. A statistically significant effect of work stress on colorectal cancer risk was observed in North America (RR = 1.51, 95% CI: 1.23-1.86, but not significant in Europe (RR = 1.16, 95% CI: 0.90-1.48). By contrast, a significant association between work stress and esophagus cancer was found in Europe, but not in North America. In addition, we did not observe any association between work stress and the risk of prostate, breast, or ovarian cancers. Findings of our study show that work stress is an important risk factor for colorectal, lung, and esophagus cancers. General public should be aware of the increased risk of cancer in employers with work stress. More efforts should be focused on understanding and studying the potential mechanisms which would help to identify employees at higher risk of these cancers.