La1-xRxMnO3 (R = Ce or Pr) exhibit valence fluctuations (R3+ and R4+) in the A sublattice of the ABO3 perovskite structure. They also display a metal-insulator (M-I) transition and magnetoresistance effect even without the substitution of divalent cations. In La1-xCexMnO3, as Ce concentration increases (x = 0.05 to 0.6), the magnitude of resistivity decreases and the magnetic transition temperature, Tc, shifts towards higher temperature. The change in transport properties is attributed to the increase in Mn3+-Mn4+ pairs. The electronic and magnetic phase diagram is obtained for La1-xCexMnO3 from the resistivity and dc susceptibility measurements over a broad range of temperature and concentrations. The thermopower and magnetoresistance are also measured for La1-xCexMnO3 for two x values (x = 0.3 and 0.6). The high temperature thermopower data fit to an adiabatic small polaron hopping mechanism.