Background: Leptospirosis is a disease caused by pathogenic bacteria called Leptospira, which is transmitted directly or indirectly. There were many of Leptospirosis study. However, the relation between demographic characteristic, occupational health and safety, and environmental factors foccusing on the workers of informal sectors was unclear. The objectives of study were to measure the association between demographic characteristics, Occupational, Health and Safety, and environmental factors with Leptospirosis in the workers of informal sectors.Methods: An observational study with case-control design. Popupation of the study were all of workers of the informal sectors in Semarang City, it is including, but not limited to farmers, cleaning worker, laborers (farming, construction, handyman) and traditional market worker. Sample of the study were 82 persons, consist of 41 cases and 41 controls. Sample were taking by consecutive sampling. Data analysis perform by univariant, bivariant, and multivariant.Results: The main risk factors were age (18–40 years old) p=0,017; aOR=42,22;95%CI=1,96- 906,55; Gender (male) p=0,017; aOR=37,01, 95%CI=1,9- 718,6; history of open wound during working p=0,042; aOR=10,85; 95%CI=1,08-108,24; home sanitation (poor, with score <60%) p=0,025; aOR=25,25; 95%CI=1,5-423,3; and history of contact with the source of infection p=0,003; aOR=56,98; 95%CI=3,8-849,2.Conclusion: Demographic characteristics, Occupational, Health and Safety, and environmental factors were associated with Leptospirosis.