The assessment of socio-economic effects of marine protected areas on fishing activity points out some methodological difficulties. As a methodology we propose a selection of two components: the fishing unit profitability and the fishery household income distribution and a comparison between a marine protected area versus an "unprotected zone". The methodology has been applied on a case study: the Chumphon National Park versus the Chumphon Province (Gulf of Thailand). Three phases have been implemented: a bibliographical analysis, the carrying out of village monographs, the carrying out of a sample-based survey. The sample-based survey results are presented as follows : the characterization of categories of the variable "marine protected area" by quantitative variables, a multivariate analysis, the performance of Chi-square tests on the relationship between a "profit per fishing day" variable divided into two categories ("in or around MPA" and "remote from the MPA", the measurement of the concentration of income or operating profit per fishery household and the Lorenz curves.