This study is focused on experimental investigation of the effect of gamma-ray irradiation on early-age cement mortar properties. Several working hypotheses were formulated based on the current research review. The results of the performed experiment in terms of the relative weight and the relative length change are described in detail in this study. Two observations could be made from comparison of the working hypotheses with the obtained experimental results. Firstly, the positive effect of gamma-ray irradiation in terms of the relative weight change was observed within the first 300 hours or within the equivalent absorbed irradiation dose of 450 kGy. Secondly, the shrinkage due to gamma-ray irradiation was smaller for the unsealed samples due to presence of carbon dioxide in the air, which is needed for the carbonation reaction. It is believed that the obtained experimental data themselves provide a platform for validation of related numerical models.