Background and Objectives: Even though most of the thyroid cancer shows good prognosis, de-differentiated thyroid cancer is still refractory to conventional treatments. Recently, kinase inhibitors including multi-kinase and BRAF inhibitors are widely used for treatment of de-differentiated thyroid cancers, but resistant to single kinase inhibitor treatment eventually encountered. Therefore, combination therapy may have better therapeutic effect than single therapy for thyroid cancer. In this study, we evaluated therapeutic effect of multi-kinase and BRAF inhibitor combination to anaplastic thyroid cancer cell lines with and without BRAF mutation. Materials and Methods: We used anaplastic thyroid cancer cell lines with BRAF V600E mutation (8505C) and with NRAS mutation (HTh7). Both cell lines were treated with various concentration of multi-kinase inhibitor (lenvatinib) and BRAF inhibitor (vemurafenib). And combination of various concentration of both kinase inhibitors were used to treat both cell lines. Cytotoxic effect was assessed with cell counting kit-8 and therapeutic effect of single kinase inhibitor therapy and the combination therapy was compared. Results: Anti-proliferative effect of vemurafenib on 8505C BRAF V600E -mutated cells was demonstrated from 0.25 μM concentration. However, HTh7 cells with NRAS mutation represented drug resistance up to 4 μM of vemurafenib. In case of lenvatinib treatment as a multi-kinase inhibitor, 8505C and HTh7 cells showed decreased cell viability dose-dependent manner. Combination treatment with vemurafenib and lenvatinib showed synergistic cytotoxic effect in BRAF mutated 8505C cell line, even at lower concentrations. Conclusion Combination treatment with multi-kinase inhibitor and BRAF inhibitor showed promising therapeutic results in BRAF mutated anaplastic thyroid cancer cell line.