In this study, radon concentration measurements were carried out by using nuclear-etch track detectors (CR-39) in the Armutcuk underground coal mine in the Zonguldak bituminous coal basin located on the West Black Sea region in Turkey. Measurements were performed between March and September 2006. Radon levels fluctuated between 63 - 706 Bqm(-3) in spring, and between 37 - 426 Bq m(-3) in summer. The average radon concentrations have been found to be 238 Bq m-3 for spring and 161 Bq m(-3) for summer. These concentrations are below the action level of 500-1500 Bq m(-3) recommended by the International Commission on Radiological Protection (ICRP-65, 1993). The mean effective dose values for workers of the mine were obtained to be 4.64 mu Sv per day for spring 2006 and 6.85 mu Sv per day for summer 2006.