The polar acidic compounds in the lately found Cambrian formation shale from Tarim Basin have been characterized by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). These marine type I source shales have different thermal maturation levels. The acidic species occurred in the bitumen of source rocks are mainly O-2, O-3, O-4, and O-5 compounds. Results of FT-ICR MS suggest the production of n-alkanes from fatty acids during diagenesis and thermal maturation. High abundance of C-32 hopanoic acid has been tentatively identified in several samples. Results clearly show the compositional dependence of acidic compounds on the thermal maturation levels of source rocks. O-2 class species gradually increase, together with the decrease of O-3 and O-4 class species with the increasing maturation, which also enhances the condensation degrees and decreases the alkylation degree of the acidic compounds in shale. These effective source rocks represent the promising ultradeep exploration potential of the Cambrian formation in Tarim Basin. This work may contribute to deeper understanding of origin, migration, and charge histories of crude oils in Cambrian petroleum system in Tarim Basin.