An experimental investigation was performed on Marangoni effect of cracked liquid film of aqueous Na_2SO_4 flowing over a vertical heated plate by using a sensitive infrared imaging technique. The results show that the thermal and solutal Marangoni effects, which result from the non-uniform distributions of surface temperature and concentration of the film, respectively, occur in the streamwise and transverse directions of the film, generating different influences on the film heat transfer. Taking account of the Marangoni number (Ma) and the solution concentration (c_0), a correlation of the Nusselt number (Nu) for the cracked liquid film is proposed. An experimental investigation was performed on Marangoni effect of cracked liquid film of aqueous Na_2SO_4 flowing over a vertical heated plate by using a sensitive infrared imaging technique. The results show that the thermal and solutal Marangoni effects, which result from the non-uniform distributions of surface temperature and concentration of the film, respectively, occur in the streamwise and concentration directions of the film, respectively different dominant on the film heat transfer. Nusselt number (Nu) for the cracked liquid film is proposed.