Interleukin (IL)-15 is an important proinflammatory cytokine that can protect epidermal keratinocytes (KCs) from ultraviolet-induced apoptosis and plays a role in the pathogenesis of psoriasis. However, the impact of IL-15 on KC differentiation remains unknown. In this study, isolated human primary epidermal KCs were treated with various concentrations of IL-15 for different times, and the expression of differentiation markers (keratin 1, involucrin and loricrin) and p53 as well as the activation of ERK, AKT and Notch induced by IL-15 in the absence or presence of Ca2+ was detected by real-time PCR and Western blot. The results showed that stimulation with Ca2+ alone increased the expression of KC differentiation markers and p53 and promoted the activation of Notch1. Pretreatment with IL-15 resulted in a decrease in the Ca2+-induced expression of KC differentiation markers and p53. Additionally, Ca2+ continually inhibited the phosphorylation of ERK1/2 and activated AKT, and IL-15 reduced the effect of Ca2+ on ERK1/2 and AKT. FR180204, a specific inhibitor of ERK1/2 phosphorylation, slightly attenuated the effect of Ca2+ on the expression of differentiation markers and p53 and the activation of Notch1. In contrast, MK-2206, an inhibitor of pAKT, strongly blocked the expression of the differentiation markers and p53 and the activation of Notch1. An anti-IL-15 antibody neutralized the effect of IL-15 on KC differentiation. These results indicate that IL-15 inhibits the Ca2+-induced differentiation of KCs, mainly via the attenuation of Ca2+-stimulated PI3K-AKT signalling.