Alimosho Local Government Area (LGA) is the most populated LGA in Lagos state. Recently, flooding has devastated lives and properties, hampering residents' daily activities when rain falls. This research adopts geospatial techniques and Multi- Criteria Decision Analysis (MCDA) to map out areas vulnerable to flood and to evaluate flood mitigation measures in the study area. Satellite images (such as topographic maps, Shuttle Radar Thematic Mission (SRTM)), Rainfall data (GCM), Landsat TM (2005), and OLI (2015) were acquired to get five criteria i.e Slope, Annual Mean Rainfall (AMR), density, Digital Elevation Model (DEM) and Land Use / Land cover (LULC) which are perceived to influence flooding, and they were subsequently ranked according to their importance using ArcGIS and Erdas Imagine, respectively. The analytical Hierarchy Process (AHP) approach was used to assign weight to the factors used for the multi-criteria analysis. The weighted sum analysis overlaid the processed maps to generate the flood vulnerability map. The result shows that most areas in Alimosho LGA are vulnerable to flooding in various degrees.