Aim: Several studies suggest that coal miners are under risk of severe health problems such as cardiovascular, pulmonary, neurological, renal, hematological and musculoskeletal disorders. However, there are limited data on biochemical changes in underground workers. In our study we aimed to evaluate the association between serum homocysteine (Hcy), vitamin B-12, cystatin C and folate levels in the blood of underground coal miners. Materials and Methods: Eighty one coal miners who work as underground or surface workers were recruited into our study. The study population was divided into two groups: the surface worker group (control group, n=33) and the underground worker group (n=48). The folate, vitamin B-12, Hcy, cystatin C levels and body mass indexes (BMI) of both groups were measured and compared. Serum folate, Hcy and vitamin B-12 levels were measured with a competitive chemiluminescence immunassay. Serum levels of cystatin C were determined by the latex particle-enhanced turbidimetric method using a cystatin C kit. Urea values were measured with a kinetic method on an automated analyzer. Results: There were no statistically significant differences between the underground workers and surface workers in the urea, cystatin C and vitamin B-12 levels. High serum Hcy levels and low folate levels were found in underground workers compared with those in surface workers. The correlation between Hcy and folate levels was also statistically significant. Similarly, there was also a significant correlation between Hcy and vitamin B-12, and between Hcy and cystatin C levels. Conclusions: Elevated Hcy levels may be associated with underground working but further research is necessary to understand the relation between elevated Hcy and increased prevalence of health problems in coal miners.