Hepatocellular carcinoma (HCC) is a highly aggressive malignancy characterized by its high resistance to chemotherapeutic agents leading to high morbidity and mortality rates. Capsaicin, the active ingredient of hot peppers, has been reported for its potential as an active anti-cancer agent. In this study, we hypothesized that incorporating capsaicin into nanocarriers might improve its pharmacokinetics. As a result, densely dispersed capsaicin-loaded trimethyl-chitosan nanoparticles (CL-NPs) were developed and their anti-tumor effect was investigated in comparison with capsaicin on human HepG2 cells. The CL-NPs were obtained via ionotropic gelation of cationic trimethyl chitosan (TMCS). Both synthesized TMCS and TMCS-based nanoparticles were characterized using zeta analyzer, nanosizer, and TEM. Human hepatoma cell line (HepG2) were cultured then divided into 4 groups receiving ethanol, conventional capsaicin, plain nanoparticles (PNs), or CL-NPs in dose of 100 µM. The apoptotic activity in the cell line was evaluated by DNA fragmentation assay, immunocytochemistry for caspase-3 and BCL-2, in addition to gene expression studies of BCL-2, and Bax genes via RT-PCR. The capsaicin effect on HCC response to chemotherapy was also assessed by studying the level of MDR-1 (multidrug resistance) gene expression. CL-NPs in dose of 100 µM, 24 h after treatment, showed more upregulation of Bax and downregulation of both BCL-2 and MDR-1 genes in comparison with conventional capsaicin. In addition, immunocytochemistry assay revealed that both capsaicin and plain NPs show higher expression of caspase-3 and lower expression of BCL-2 than the control group, while the group treated with CL-NPs showed complete necrosis. This indicates that plain TMCS nanoparticles had a little anti-apoptotic effect by themselves. Our findings highlight the potential of the developed CL-NPs as an effective anti-cancer agent which efficiently induced apoptosis in human HepG2 hepatocarcinoma cells. Moreover, a possible role in improving response to chemotherapy has been observed through downregulation of MDR-1 gene. dermatological inflammatory-associated diseases [11-18]. Moreover, the anti-cancer effect of capsaicin has been a hot area of research. In recent years, capsaicin has been used in suppressing the carcinogenicity of many types of tumors as: lung, prostate, breast, gastric, pancreatic, colorectal, and osteosarcoma [19-26].