This checklist serves as a guidebook for plant enthusiasts to access the list of tree species occurring in Sabah. This checklist includes 3,173 species, 122 infraspecific, 592 genera and 125 families of native, as well as the most common introduced trees. It also provides general information about ecology and distribution of interesting trees in Sabah. This checklist consists of two parts, namely tree family and tree species checklist. The tree family checklist provides list of tree family, number of genus, species, endemic species, introduced species and infraspecific for each family. The species checklist provides list of tree species, information on vernacular names, size, geographical distribution, regional distribution, habitats, secondary forest species and conservation status of species.