Abstract: Traditionally, it is believed that kerogen, a organic matter insoluble in organic solvents separated chemically from source rock, is a material for hydrocarbon generation¹.The procedure to treat samples as such, however, may destroy the original occurrence and relationship between organic matter and clay in source rocks. We extracted an organo-clay complex (<2μm) from the crushed source rocks in the depth of 280~3 500 m, in the Jiyang sag, East China. The complex is mainly composed of layered illite-smectite (I-S) and illite with a value of TOC up to 2.62%~9.78%. After treatment with H₂O₂, TOC remains as high as 1.23%~4.63%, suggesting that it is the components in which organic matters are enriched. The diffraction peak (d₀₀₁) of the complex is 1.3~1.4nm at 250℃, and moves to 1.0 nm at 550℃ in XRD curves, and the exothermic peaks of the complex is extraordinary stable at 350℃ in DTA curves.; The result is consistent in both the XRD and DTA observations. It indicates that organic matter can enter the interlayer space of clay minerals. With PY-GC analysis, the organic matter of C₅ and C₂₅ is released from the complex in a temperature range of 250~650℃, and reaches a peak at about 450℃. Our findings reveal that organic matter can enter interlayer of clay minerals forming a kind of natural and highly stable organo-clay complex, and the composition of the organic matter in the complex is similar to the crude oil. As a kind of natural material, the organo-clay complex plays an important role in hydrocarbon generation in source rocks.