The efficient delivery of antisense oligonucleotides (ASOs) to the targeted cells and organs remains a challenge, in particular, in vivo. Here, we investigated the ability of a library of biodegradable lipid nanoparticles (LNPs) in delivering ASO to both cultured human cells and animal models. We first identified three top-performing lipids through in vitro screening using GFP-expressing HEK293 cells. Next, we explored these three candidates for delivering ASO to target proprotein convertase subtilisin/kexin type 9 (PCSK9) mRNA in mice. We found that lipid 306-O12B-3 showed efficiency with the median effective dose (ED50) as low as 0.034 mg·kg-1, which is a notable improvement over the efficiency reported in the literature. No liver or kidney toxicity was observed with a dose up to 5 mg·kg-1 of this ASO/LNP formulation. The biodegradable LNPs are efficient and safe in the delivery of ASO and pave the way for clinical translation. Keywords: antisense oligonucleotide, biodegradable lipid nanoparticle, PCSK9