In this study we measured radon (Rn-222) concentrations in offices at the Me elik campus of Eskisehir Osmangazi University to estimate the effective dose of Rn-222 and its progeny for office occupants. The measurements were performed four times in 2011 over a period of 3 months using solid state nuclear track detectors (LR-115). A total of 381 LR-115 detectors were installed in 110 different offices, choosing three offices on each floor in the same building. Rn-222 concentrations obtained in the first, second, third, and fourth measurement periods were 163 (73) Bq m(-3), 105 (53) Bq m(-3), 77 (43) Bq m(-3), and 164 (70) Bq m(-3) respectively. The Rn-222 concentrations and seasonal Rn-222 variations in the offices were similar to those found in dwellings in Eskisehir. The total annual effective dose was estimated to be 3.398 mSv y(-1).