The purposes of this inter-related study were to test a structural equation model of factors affecting Thai tourist loyalty toward Marine National Parks in Southern Thailand. The subjects of the study were 800 Thai tourists who visited Marine National parks in Southern Thailand, selected by using accidental sampling. The research hypothesis included five major factors causing tourist loyalty, in addition to some latent variables: corporate social responsibility, destination image, perceived value, tourist satisfaction and tourist complaints. The results revealed that destination image, perceived value, tourist satisfaction and tourist complaints directly affect tourist loyalty, whereas the indirect factors affecting tourist loyalty include corporate social responsibility, destination image, perceived value and tourist satisfaction.