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Resistance to anti-cancer drugs is one of the main factors of treatment failure resulting in high morbidity. Among the reasons of resistance, overexpression of efflux pumps leading to multidrug resistance is an important issue that needs to be solved. <i>Taiwanofungus camphoratus</i> has been used as a nutritional supplement to treat various cancers. However, its effects on the resistance to chemotherapeutic agents are still unknown. In this study, we report four new chemical constituents of <i>T. camphoratus</i> isolated from an ether extract: camphoratins K (<b>1</b>) and N (<b>2</b>) and benzocamphorins G (<b>3</b>) and I (<b>4</b>). Furthermore, we evaluated zhankuic acids A&#8722;C for their P-glycoprotein (P-gp) inhibitory effects. The results showed that zhankuic acid A was the most potent P-gp inhibitor compound and (at 20 &#956;M) could reverse drug resistance in human cancer cells, restoring an IC₅₀ of 78.5 nM for doxorubicin, of 48.5 nM for paclitaxel, and of 321.5 nM for vincristine, indicating a reversal fold of 48, 38, and 45 times, respectively. This study provides support for the use of <i>T. camphoratus</i> in the further development of cancer therapy.