The Middle Jurassic volcanic rocks of Haifanggou Formation in western Liaoning are intermediate-acid igneous rocks of the trachyandesite-trachyte-andesite-dacite assemblage. The volcanic rocks are close to calc-alkaline and high-K calc-alkaline series，and their whole rock Rb-Sr isochron age is 177.2±28.0 Ma. They are enriched in Al (Al2O3≥15.45％) and Na (Na2O/K2O≥1.35), and SiO2≥56.99％．They are characterized by strongly fractionated REE［(La/Yb)N≥14.80，(Ho/Yb)N≥1.15］, low Yb and Y(Yb≤1.42×10-6，Y≤15.18×10-6)，absence of Eu negative anomaly(0.86～1.03)，obvious depletion of Rb, Nb, Zr and Ti, relative enrichment of Sr, Ba, K and LREE，and low Rb/Sr ratios(＜0.1)．These volcanic rocks are geochemically similar to adakite，and are hence regarded as adakite-like rocks．The Sr, Pb and Nd isotopic data indicate that they were derived from the partial melting of ancient intermediate-basic metamorphic rocks in the lower crust，and thedepth of volcanic sources must have been very great．Studies show that the volcanic rocks were formed in an intraplate setting, with no direct relationship with the westward subduction of the Pacific plate． The lithospheric delamination must have been related to the obvious transformation of the Mesozoic tectonic stress field，the intense volcanic-magmatic activities and the formation of abundant fault basins in western Liaoning．The adakite-like rocks of Haifanggou Formation are of important geological significance in the study of magma derivation，crust-mantle process and geodynamics.