Introduction: The plant, Astilboides tabularis (Hemsl.) Engler, is used in Chinese and Korean medicine to regulate blood sugar levels; however, little is known about its precise effects. Materials and Methods: In this study, we aimed to measure the composition as well as the antioxidant, and anti-proliferative capacities of A. tabularis. Various extracts were generated using different organic solvents, and in vitro antioxidant activities were evaluated using DPPH free radical-scavenging and reducing power assays. The extracts were also evaluated based on their ability to inhibit lipopolysaccharide (LPS)-induced Nitric Oxide (NO) production in RAW 264.7 cells. Results: Research shows that the A. tabularis ethyl acetate (EtOAc) extract showed significant antioxidant activity. Additionally, this extract could inhibit the LPS-induced expression of inflammatory mediators and pro-inflammatory cytokines in RAW 264.7 cells, including inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and interleukin-1 beta (IL-1ß). Notably, the A. tabularis EtOAc extract also displayed potent cytotoxic effects against MCF-7 and HeLa cancer cell lines, as determined by MTT assays. Lastly, total phenol and flavonoid content was measured for all extracts, and four flavonoid compounds-catechin, kaempferol, quercitrin, and isoquercetin were isolated from the EtOAc extract. Their structures were confirmed using mass spectrometry and nuclear magnetic resonance, and these isolated compounds were found to display potent DPPH free radical-scavenging activity. Conclusion: Thus, our data suggest that phenolic compounds in A. tabularis extracts promote antioxidant activity, and furthermore, these extracts show numerous features that indicate potential for therapeutic development.