Meisoindigo is an indigo natural derivative commonly used in anti-cancer therapy. In the clinical application, it was also found to have good therapeutic effect on psoriasis. In order to further understand its mechanism of action, human normal keratinocyte cell line HaCaT and RAW 264.7 were used to identify if meisoindigo could affect the inflammatory factors such as NO and other important cytokines which were highly involved in psoriasis. Our results indicated that meisoindigo decreased the production of NO in LPS-stimulated RAW 264.7 cells and reduced the expression of cytokines in LPS-stimulated HaCaT cells. And TLR4-TAK-NF-kappaB was a possible pathway mainly involved in the attenuation of iNOS and pro-inflammatory cytokine production by meisoindigo, which may take part in the therapeutic effect of meisoindigo on psoriasis.