This study was conducted to develop the suitability model and to generate site suitability maps of onion production in the province of Occidental Mindoro, Philippines. Weights and criteria were generated using Geographic Information System 10.2 ModelBuilder software as a guide in doing the crop suitability analysis. Suitability maps were generated based on the different criteria (slope, elevation, rainfall, temperature, soil texture, and landcover) of onion crop requirements and weights that are assigned to these specific criteria. Finally, site suitability maps were generated by overlaying these re-classified maps. The results of the site suitability analysis for onion showed that in the study area, 2.54% of the land area is “very high suitable”, 26.46% of the agricultural land is “high suitable”, 37.39% is “moderately suitable”, 14.07% is “low suitable”, 1.21% is “not suitable” and 18.33% fall under restricted area. These generated maps will help to identify the most suitable areas for onion production, thus the yield gaps will decline and assure food security to a greater extent. These generated maps provide information that could be used by farmers in selecting areas suitable for onion production. It will also be helpful for field workers, policymakers, and planners working in the agricultural sector.