In this study, petroleum acids were extracted from the super-heavy oil of Liaohe oilfield,North-east China, by using acetic acid, and their structural components and properties were investigated by using FT-IR and MS. Moreover, the trace metal contents in the super-heavy oil sample before and after acetic acid treatment were also measured in this work. The results showed that naphthenic acids were the main component of petroleum acids in Liaohe super-heavy oil, and the content of naphthenic acids with double tings was higher than that of other naphthenic acids. It can be concluded that petroleum acids in Liaohe super-heavy oil mainly consist of naphthcnic acids, with a carbon number of around 11-69 and containing one to six naphthenic rings and/or one to two aromatic tings, and mainly exists in form of metal salts of petroleum acid. The molecular weight of petroleum acids is in the range of 190-1000.