Neem is one of the most popular multi-purpose tree species that has been planted throughout tropical countries because it grows well on various sites with poor soil and low annual rainfall. Genetic data among Neem provenances is necessary for tree improvement program. Thus this study examined the genetic variation among 22 Neem provenances from the International Provenance Trial in Kampheng Phet province using eight isozyme systems: diaphorase (DIA), format dehydrogenase (FDH), glutamate oxaloacetate transaminase (GOT), glucose-6-phosphate dehydrogenase (G-6PDH), isocitrate dehydrogenase (IDH), malate dehyfrogenase (MDH), phosphoglucomutase (PGM), and shikimate dehydrogenase (SKDH). The 12 gene loci from these enzyme systems were found in 22 provenances. DIA-A, DIA-B, GOT, MDH-C, and SKDH showed variations between Thai and Indian Neems. GOT, G-6PDH, IDH, MDH-A, MDH-B, PGM-A, and PGM-B showed moderate to high levels of provenance variation. The average expected heterozygosity (He=0.226) and Wrights FST (0.58) were high, which indicated wide genetic variation among provenances. The genetic distances (D) between Thai and Indian Neems were high (D>1.00). However, D values within Thai Neem provenances and within Indian Neem provenances were low. This can be used in future breeding work.