The purpose of this study was to determine the condition of the underwater substrate and the location that has the potential to be developed as marine tourism (snorkelling) in Pasumpahan Island, Padang city. The research method used scoring assessment the suitability parameters of marine tourism with weighting the score. The location in this research was Pasumpahan Island waters based on waters brightness, beach type, lifeform, and underwater substrate. Based on the results of the study it can be concluded that 1) the basic substrate of Pasumpahan Island waters is a living coral area of 63,900 m² with a percentage of 25.81%, dead coral covering 75,600 m² with a percentage of 30.54%, and sand covering 108,000 m² with a percentage of 43.63%; and 2) Pasumpahan Island has a suitability category for snorkelling tours as follows, quite suitable category (S2) with an area of 64,859 m², very suitable category (S1) with an area of 117,276 m².