Abstract: Through systematic evaluation on the organic geochemical and biomarker compound features of source rocks from Jiufotang Formation in JD1 well in Jinbaotun-Jargalang region of southwestern Songliao Basin, the authors conclude that the dark mudstone belongs to poor-medium grade source rocks with organic matter of II-type kerogen in low maturity-maturity stage. The n-alkanes are dominated by unimodal distribution of "front type" with main peak carbon numbers of C18 and C19. The odd-even predominance is not prominent. The Pr/Ph ratios(0.24-0.46) and gammacerane indexes (0.11-0.32) indicate the source rocks were formed under reduction condition with freshwater-brackish water lacustrine sedimentary environment. The distribution characteristics of C27-C28-C29 regular steranes are slightly various, reflecting mixed sources of organic matters. From the above, the source rocks in the study area have certain hydrocarbon generation potential.