The critical temperature (Tc) and the isotope coefficient (a) of two-dimensional van Hove superconductors have been analyzed. The phonon induced superconductors with both weak and strong couplings are considered. For weak coupling, the variation of Tc and a as a function of average phonon frequency, wD, for three sets of pairing potential, V, shows that a decreases at nearly same rate with the increase of wD; but Tc increases with increasing wD but at different rates for different V. For strong coupling, the variation of Tc and a shows that smaller band width produces desirable results that are consistent with observation.