The development of plant-derived nutraceuticals is an increasingly popular research area, driving the exploration of well-known medicinal plants through bioprospection. Tessaria absinthioides (Ta) is a native plant from South America, which demonstrates anticancer activity. In vitro, Ta was cytotoxic against glioblastoma, adenocarcinoma, and colorectal cancer cell lines, while in vivo, its oral administration affects melanoma, colorectal, and breast cancer growth. Moreover, Camellia sinensis (Cs)—green tea—is known for its potent antioxidant and anticancer activity. This work evaluates the combination of Ta with Cs to obtain nutraceutical preparations with antitumoral properties. Ta and Cs aqueous decoctions were prepared at 5% w/v and were combined in different ratios. Cytotoxicity was determined using the MTT assay on the B16F0 cell line (non-metastatic murine melanoma; from ATCC, VA-USA) treated with Ta, Cs, and Ta+Cs (1:1, 2:1, 4:1) for 72h. The median effective dose and combination index were calculated using CompuSyn Software (values <1 indicate synergism). In vivo, C57BL/6 mice with subcutaneous B16F0-induced tumors were orally treated with Ta, Cs, or Ta+Cs (1:1), at doses of 150 mg/animal/day for 22 days; tap water was used as the control. Tumor growth was monitored daily, followed by necropsy and tumor weight measurement. Ta and Cs decoctions inhibited B16F0 cell proliferation dose-dependently, with median dose values of 1391.4 and 655.8 µg/mL, respectively. The Ta+Cs combination (1:1, 2:1 and 4:1) was synergistic, particularly at a 1:1 ratio (combination index = 0.43, 0.86, and 0.93, respectively). In vivo, Ta+Cs showed a significant decrease in tumor weight compared to the control (0.81g vs. 1.87g, respectively; ANOVA followed by Fisher’s test, p<0.0421), as well as a prolonged tumor detection time (21 vs. 14.5 days in control; Log Rank test, p=0.0088). These results demonstrate that the decoction of T. absinthioides combined with C. sinensis synergistically inhibits murine melanoma cell proliferation and exhibits a promising in vivo antitumoral activity, supporting nutraceutical preparation development as a complementary method of treatment for cancer.