Abstract. Raganas AFM, Magcale-Macandog DBM. 2020. Physicochemical factors influencing zonation patterns, niche width, and tolerances of dominant mangroves in southern Oriental Mindoro, Philippines. Ocean Life 4: 51-62. Physicochemical factors are known for having strong influence on the spatial patterns and structural complexity of mangroves. In this regard, we aimed to contribute to filling up this information gap in the six mangrove ecosystems on the southern coast of Oriental Mindoro, Philippines. In each of the six mangrove ecosystems, the dominant mangrove species were identified in four mangrove zones - seaward, riverine, middle, and landward - using a stratified random sampling method for vegetation survey. Physicochemical parameters of water, air, and soil were also obtained from these ecozones. Results of the Principal Component Analysis revealed that temperature and water salinity are the factors that show strong influence on the spatial distribution of the dominant mangrove species. Canonical Correspondence Analysis revealed that Avicennia marina, Sonneratia alba, and Rhizophora apiculata, are species associated with a highly saline environment, while Xylocarpus granatum, Ceriops decandra, Avicennia rumphiana, and Rhizophora mucronata are species associated with low to optimum saline environment. Most of these dominant species preferred ecotypes with low to optimum salinity levels as revealed by their individual niche width and tolerances. The different adaptations and dominance of these mangrove species provide insights in the identification of appropriate species that could be used as planting materials for rehabilitation endeavors in the respective mangrove ecosystem.