Abstract: The Middle to Late Jurassic is an important transitional period in the tectonic evolution of Northeast China, the study of magmatic rocks during this period is relatively limited due to its rare exposure. In this study, LA-ICP-MS zircon U-Pb geochronology and rock geochemistry were used for the first time to investigate the Middle to Late Jurassic intrusive rocks located in the southern part of the Xing'an Block, analyzing its petrogenesis and geological significance, and further constraining the closure timing of the Mongolia-Okhotsk Ocean in the southern Xing'an Block. The study shows that the intrusive rocks include two types of rock: granite porphyry and diorite porphyrite, with crystallization ages of (167.0±0.5) Ma and (160.0±0.7) Ma, respectively, indicating that they are products of Middle to Late Jurassic magmatic activities. Two rocks belong to the high-K calc-alkaline I-type series, characterized by Na₂O contents ranging from 4.57％ to 4.97％ and 3.21％ to 3.98％, and weak aluminum saturation with A/CNK ratios ranging from 1.00 to 1.07 and 0.93 to 1.10. They also have characteristics of enrichment in large ion lithophile elements (Rb, Th and K), depletion in high field-strength elements (Ta, Nb, P and Ti), moderate rare earth element contents (ΣREE) of (90.5~153.1)×10^-6 and (111.6~128.8)×10^-6, significant fractionation between light and heavy rare earth elements with LREE/HREE ratios of 6.74~10.26 and 5.14~8.84, (La/Yb)_N of 5.61~9.58 and 4.92~10.38, and middle negative Eu anomalies (δEu) ranging from 0.58 to 0.68 and 0.83 to 1.02. These results can be inferred that the petrogenesis of the intrusive rocks is likely related to the closure of the Mongolia-Okhotsk Ocean, and they formed in a tectonic background of crustal thickening collapse or detachment, during the transition from compression to extension tectonics.