Research area is located in Jambi sub basin, the northern part of South Sumatera Basin formed during Tertiary age. South Sumatera Basin, as well as the Central Sumatera and North Sumatera Basins is a basin form in the back arc belt. The propose of the research is to determine petrological characteristics of the pre-Tertiary basement rock based on major oxides analysis from the granitoid basement rock in research area with AAS method (Atomic Absorption Spectrophotometry. Thus the petrogenesis could be determined, including kinds and characteristics of parent magma. Chemical rock analysis confirm the lithology of granitoid basement in Jambi sub basin are intermediate – acid magmas, calc-alkaline, medium – high K, metalluminous, subduction-related (orogen) at active continental margin. Granitoid basement rock of JSB-4 and JSB-6 shows magnetite series and I type. This Mesozoic granitoid probably as extension from the Thailand and Burma granite province,that underline the fact that there has been a history of subduction-related magmatism along Southwestern edge of Sundaland since earliest Mesozoic times.