A series of 6-chloro-quinolin-2-one derivatives were designed and synthesized as FXIa inhibitors by exploration of 1, 1 prime and 2 prime groups. Each compound was accessed for inhibitory effect on FXIa and some of them were evaluated in the clotting assay. demonstrated excellent in-vitro potency (FXIa IC: 15 nM, 2 x aPTT: 6.8 μM) and good in-vivo efficacy (prolonged in-vivo aPTT by more than 1-fold