Differential scanning calorimetry and thermogravimetry techniques were successfully used for stability studies of capecitabine. Decreasing values of melting temperature, heat of fusion, and peak purity calculated from the Van’t Hoff equation indicated the gradual decomposition of capecitabine stored at 40 °C in 75% of relative humidity. The increase in mass loss connected with the water sorption was observed simultaneously. High performance liquid chromatography proved the results of thermoanalytical studies. Infrared spectroscopy (IR) appeared to have the lower sensitivity for the decomposition products detection.