Head and neck cancer (HNC) is one of the most common forms of cancer in Taiwan. In addition, head and neck cancer cells (HNCs) are highly tumorigenic and resistant to conventional therapy. Therefore, development of new therapeutic regimens that are adjuvant to conventional treatments would benefit future head and neck cancer therapy. In this study, we found that the lyophilized particles and ethanolic extracts of Antrodia cinnamomea mycelia inhibited the tumor growth of HNCs by xenograft assay in vivo. Moreover, administration of lyophilized particles or ethanolic extracts to nude mice did not cause significant side effects. Our study revealed that the Antrodia cinnamomea mycelia extract (ACME) efficiently inhibited the tumorigenicity of HNCs without causing organ failure. Furthermore, it showed that ACME may work as a novel drug candidate for alternative treatments for head and neck cancer.