“Forester’s manual of Dipteroracps” written by Symington compiles floristic information of dipterocarps in Peninsular Malaysia, and provides our knowledge about dipterocarp flora in Peninsular Malaysia. However, there are few studies that have attempted to analyse the floristic information of dipterocarps. Here, we have developed a GIS database of dipterocarp flora of forest reserves in Peninsular Malaysia using Symington’s data. A cluster analysis showed geographically recognizable floristic regions of dipterocarps: northern area, eastern part and the others. We found significant relationship between floristic composition and environmental factors among the forest reserves. The similarity of floristic composition was significantly related to both geographical distance and several environmental factors, and our results also suggested that rainfall seasonality is an important factor to explain the floristic pattern of dipterocarps in Peninsular Malaysia. We will discuss how the environmental factors correlate with the floristic pattern of dipterocarps in Peninsular Malaysia.