Bioavailability of active compounds extracted from herbs is generally limited to be adsorbed or expressed to target organisms due to several physical and chemical factors. Nanoparticle encapsulation techniques was developed to carry bioactive macromolecules of Centella asiatica (Buabok) in the form of C. asiatica Extract-loaded Bovine Serum Albumin Nanoparticles (CBNPs) to improve bioavailability. In this study, the antioxidant activities of CBNPs and C. asiatica crude extract were evaluated by using DPPH radical scavenging assay in the simulated gastrointestinal system, including mastication, stomach, duodenum, and ileum conditions to provide the environment which similar to in vivo system in terms of chemical and physical parameters. CBNPs were prepared by mixing of C. asiatica crude extract and BSA at different ratio of 1:2, 1:3, and 1:4. The results showed that the highest antioxidant activity of CBNP was observed when the ratio of crude extract and BSA at 1:2 was used at pH 2.0 or in the simulated stomach condition. The denaturation or unfolding of BSA in the simulated stomach occurred when pH was low could lead to the release of active compounds at certain area in gastrointestinal system.