Thiolane steroids can provide abundant geochemical information as long as their molecular structures, biological origins, formation pathways, sulfurization environments and sulfurization timing are understood. Steroids in saturates, aromatics and sulfidic fraction are investigated in five low-mature sulfur-rich oils in Huanghekou Depression, Bohai Bay Basin. The high abundances of C27 sterane, C30 4-methylsterane, dinosterane and triaromatic steroids indicate the abundant dinoflagellate and other algae inputs. In addition, the distribution of C29 steranes is also influenced by the unique algae inputs. Algae blooms offer abundant precursors of steroids for sulfurization. Two types of thiolane steroids were identified in the oils: (i) thiophane ring merging at D-ring and (ii) thiophane ring at side-chain of steroids. The double bonds at C-22 position of precursors are crucial for intramolecular sulfurization of steroids. Therefore, the C28 and C29 steroids are easier to form thiolane steroids in type I than C27 species, further, C30 species are mostly transferred to counterparts in type II via isomerization and H2S addition/elimination. Thiolane steroids are diagenetic products, and the saline lacustrine, with stratified water column, might be the suitable depositional environments for formation of thiolane steroids. Even though the evolution pathways occur under the sulfur-rich conditions, the thiolane steroids are still sensitive to the reducing environments, resulting in good correlations between parameters of the percentage of C27 thiolane steroids, (C28a + C29a)/C27a and biomarkers that indicate reducing environment.