The adsorption of organic matter(OM)onto clay minerals has long been considered as a significant way of OM preservation in source rock.Here we analyzed the relationship between OM and the specific surface area(SSA)of <2μm clay size fraction isolated from 13 source rock cores collected from Dongying depression.Rock-Eval pyrolysis and N2 adsorption experiment were employed to probe the characteristics of OM and SSA(denoted SBET)in samples before and after OM extraction using trichloromethane.The results indicate that various kinds of OM occurrence coexist in clay size fraction and their contributions to hydrocarbon are different in each period of OM evolution.The occurrence and amount of OM affect the S BET of clay size fraction,and a nonlinear negative correlation between total organic carbon(TOC)and S BET can be recognized.The soluble OM(chloroform extract “A”),mainly stored in the pore space of clay size fraction,shows a negative correlation in amount with S BET.Our data also indicate that free hydrocarbon(S1)was stored mainly in the pore space and/or the surface of clay size fraction,whereas pyrolysis hydrocarbon(S2)was mingled mainly with clay minerals.Therefore,to understand various OM occurrences and their relationship with SBET in the clay size fraction is significant in the study of generation,accumulation,and migration of hydrocarbon in muddy source rock. The adsorption of organic matter (OM) onto clay minerals has long been considered as a significant way of OM preservation in source rock. Here we analyzed the relationship between OM and the specific surface area (SSA) of <2 μm clay size fraction from 13 source rock cores collected from Dongying depression. Rock-Eval pyrolysis and N2 adsorption experiment were employed to probe the characteristics of OM and SSA (rendered SBET) in samples before and after OM extraction using trichloromethane. the results that indicates that various kinds of OM occurrence coexist in clay size fraction and their contributions to hydrocarbon are different in each period of OM evolution. the occurrence and amount of OM affect the S BET of clay size fraction, and a nonlinear negative correlation between total organic carbon (TOC) and S BET can recognized.The soluble OM (chloroform extract “A ”), mainly stored in the pore space of clay size fraction, shows a negative correlation in amount with S BET. Our data also indic ate that free hydrocarbon (S1) was stored mainly in clay pore size and / or the surface of clay size fraction, whereas pyrolysis hydrocarbon (S2) was mingled mainly with clay minerals.Therefore, to understand various OM occurrences and their relationship with SBET in the clay size fraction is significant in the study of generation, accumulation, and migration of hydrocarbon in muddy source rock.