Abstract: Objective To examine the prevalence and multimorbidity of chronic diseases and health loss related to the diseases among employees engaged in field operation in large oil fields.Methods A face-to-face survey was conducted among 1 964 employees engaged in field operation at several work areas of a large oil field using a questionnaire on personal health.Health loss was assessed with duration of chronic diseases,long-term medication,and the scores of Euro-Quality of Life-5 Dimension (EQ-5D)and self-rated health.Binary logistic regression was used to analyze risk factors.Results Of all the employees,765 (39.0%),303 (15.4%),and 139 (7.1%) reported suffering from at least one,two or more,and three or more chronic diseases,respectively.Among the employees with multimorbidity,the main comorbidities were hypertension and hyperlipidemia,hypertension and coronary heart disease,osteoporosis and hyperlipidemia,osteoporosis and hypertension,gout and hypertension,and diabetes and hyperlipidemia.The employees with coronary heart disease,gout,obesity,and rheumaimmune diseases showed lower scores of EQ-5D and self-rated health.There were 24.4% of the employees reporting long-term medication and of the medicines used for long-term medication 48.7% were drugs for cardiovascular diseases.Logistic regression analyses showed that gender,age,smoking,alcohol drinking,mental stress,sleep quality were major influencing factors for the prevalence of chronic diseases.Conclusion Nearly half of the oil filed employees engaged in field operation suffered from chronic diseases,including hypertension and osteoporosis,and multimorbidity of the diseases;the results suggest that more concerns should be paid on chronic disease prevention and health promotion among the employees.