Abstract: The influence of particle size on oil yield from pyrolysis of Huadian oil shale was investigated. The raw material was crushed and sieved to 6 fractions with different particle size: <0.074, 0.074~0.125, 0.125~0.25, 0.25~0.5, 0.5~1 and 1~3 mm. Then, the fraction of 0.25~0.5, 0.5~1 and 1~3 mm were ground to obtain the corresponding powder samples. A standard method and thermogravimetric analysis were applied to measure and characterize the oil yield and organic matter content in different samples. The results show that both the oil yield (from 11.92% to 6.14%) and organic matter content decrease gradually with decrease in particle size, and a significantly linear relationship is observed between oil yield and organic matter content. The oil yield for powder sample of 0.25~0.5, 0.5~1, and 1~3 mm decreases, while gas yield increases, but the variation is slight and below 1%. Both preferential distribution of organic matter and secondary reaction of shale oil determine the oil yield of fractions with different particle sizes. Furthermore, the selective enrichment of organic matter is the predominant factor.