Pollen materials from seventy euphorbiaceous species in Thailand were treated by the acetolysis method. The acetolysed pollen grains were studied on morphology by means of light and scanning electron microscopes. Pollen descriptions, key to pollen types, photomicrographs of all studied species and the phylogenetic trends based mainly on pollen morphology had been presented. The herbarium specimens and pollen-type slides were kept in the Professor Kasin Suvatabandhu Herbarium, Chulalongkorn University (BCU). Fifteen pollen types are recognised based mainly on apertures and ornamental patterns. The aperturate pollen grains are 3-colpate type, 3-colporate type, 4-(5)-colporate type, 7-11-heterodiploporate type, and pantopolyporate type. The majority of the studied pollen is 3-colporate type. This pollen type has colporate aperturation possibly have diverse exine sculpturing which vary from ornamentation with projecting elements (granules, scabrae, baculae and clavae) to perforation, reticulation and striation. Whereas all inaperturate type and 3-colpate type have "croton pattern" which show distinctive projecting elements on the exine. It is ascertained that pollen morphology of the family Euphorbiaceae can be of taxonomic value and as the supporting evidence to the morphological study and phylogenetic study.