Psoriasis is a chronic inflammatory skin disease with high morbidity, poor treatment methods and high rates of relapse. Keratinocyte hyperproliferation and shortened cell cycles are important pathophysiological features of psoriasis. As a known oncogene, Yes-associated protein (YAP) plays a role in promoting cell proliferation and inhibiting cell apoptosis; however, whether YAP is involved in the pathogenesis of psoriasis remains to be determined. Amphiregulin (AREG), a transcriptional target of YAP, was found to be upregulated in psoriasis, and overexpression of AREG promoted keratinocyte proliferation. In the present study, immunohistochemistry showed that YAP expression was elevated in the skin of psoriasis patients and in the Imiquimod (IMQ) mouse model of psoriasis. Knockdown of YAP in HaCaT cells inhibited cell proliferation, caused cell cycle arrest in G0/G1 phase and promoted apoptosis. These changes in YAP-knockdown HaCaT cells were related to changes in AREG expression. We concluded that YAP may play an important role in the regulation of abnormal keratinocyte proliferation via an AREG-dependent pathway and that YAP could be a new target in the treatment of psoriasis.