The O - C curve of the eclipsing binary U Sagittae was analyzed using the Kalimeris method. A period decrease was indicated by this curve. The observed period P(E) and its rate of change dP/dE as a function of time were calculated. To reveal any cyclic period variations, the P(E) function was subjected to Fourier analysis. A cyclic period change of 9.5 yr duration with amplitude ΔP = 6.385 × 10^-6 days was obtained. The mass transfer rate for the system was calculated, and these results have been used to discuss period variability.