Abstract: The microstructure and mechanical properties of 0.21C-1.43Si-1.35Mn steel heated by a quenching and partitioning (Q&P) process in the two-phase region and the full austenite region were investigated. The results show that if heating the steel in the two-phase region, the microstructure consists of martensite, retained austenite and ferrite, and the tensile strength, elongation and strength ductility are 1013 MPa, 25% and 25 655 MPa·%, respectively. While heating the steel in the full austenite region, the micro-structure consists of martensite and retained austenite, and the tensile strength, elongation and strength ductility are 1 257 MPa, 17% and 21 454 MPa·%, respectively. There is mainly lath martensite along with high-density dislocations in the Q&P steel. A few twinning martensite transformed after partitioning can be observed as well. Retained austenite with a volume fraction of 10. 67%, distributed within lath martensite, can be acquired in the shape of films after the Q&P process.