La0.67Ca0.33MnO3 (LCMO) films are epitaxially grown on (0 0 1) SrTiO3 substrate using pulsed laser deposition technique. The effect of LaMnO3 (LMO) buffer layer on the microstructure and growth mode of LCMO films is studied. It is found that the 30-nm-thick LCMO films with and without a LMO buffer layer follow a layer-by-layer growth mode. The difference is that some dislocations are observed in LCMO film without a LMO buffer layer, while no evident defects are produced in LCMO film with a LMO buffer layer. Besides, for the film with a LMO buffer layer, the effect of film thickness on film growth mechanism is also investigated. It is observed that the LCMO films transform from a layer-by-layer growth mode to a layer by layer plus an island (columnar) growth mode as the film thickness increases from 30 nm to 460 nm. A growth model is introduced to explain the effect of LMO buffer layer and film thickness on the growth mechanism of LCMO films. The results can shed light on the growth mechanisms for other perovskite epitaxial films with buffer layers.