Results are presented of the orbital period analysis of two Algol-type binary stars (AV Cep and GI Cep). All available minima times in the literature together with minima times obtained in this study were used. The orbital period changes were investigated using the O-C method. O-C diagrams of both systems show upward parabolic variations, which indicate that the orbital period of these two systems is increasing secularly. The rate of period increase of AV Cep and GI Cep was calculated to be 0.415 +/- 0.016 s/year and 0.026 +/- 0.009 s/year, respectively. These secular period increases could be explained in terms of mass transfer from the secondary component to the primary component according to the classic Algol scenario.