In this study we measured radon (222 Rn) concentrations in offices at the Meşelik campus of Eskişehir Osmangazi University to estimate the effective dose of 222 Rn 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. 222 Rn 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 222 Rn concentrations and seasonal 222 Rn variations in the offices were similar to those found in dwellings in Eskişehir. The total annual effective dose was estimated to be 3.398 mSv y −1 .