The Bilong Co oil shale is located in the southern part of the Qiangtang basin. This oil shale zone, together with the Shengli River-Changshe Mountain oil shale zone in the northern part of the Qiangtang basin, represents a large marine oil shale resource in China. An organic geochemical investigation of the oil shale was performed to reconstruct paleoenvironment during deposition and to assess petroleum prospects. The TOC content (6.75-19.2 wt.%) and S(2) values (5.96-70.2 mg HC/g rock) of oil shale samples from the Bilong Co area are relatively high indicating that the oil shale from the Bilong Co area has shale oil producing potential. The thermal maturity assessed from T(max) and other maturity-related parameters (Ts/(Ts+Tm), C(32)Hop S/(S+R), C(29)St S/(S+R), and C(29)St beta beta/(alpha alpha+beta beta)) shows a mature stage of the organic matter. Analyzed oil shale samples from the Bilong Co area are characterized by a dominance of low carbon number molecular compositions with relatively high C(21-)/C(21+) (0.82-1.95), low Pr/Ph (0.13-0.80), high concentrations of homohopanes (C(31)-C(35)), and a slight predominance of C(29) steranes, indicating reducing environments, highly saline conditions, a strong contribution of inferior aquatic organisms, and some influence of terrestrial organic matter. Highly similar biomarker characteristics between the Bilong Co oil shale and nearby Zharen-Longeni crude oil in the southern Qiangtang depression suggest that the oil shale from the Bilong Co area has made a strong contribution to the generation of Zharen-Longeni crude oil.