An organ fibrosis inhibitor, in particular, a liver fibrosis inhibitor is provided, which contains histidine, preferable together with cysteine and/or cystine as active ingredients. Owing to the combined use, a remarkable effect of inhibiting organ fibrosis, in particular, liver fibrosis can be shown. These substances are usable as the desired active ingredients in the form of a drug or in the form of a food and drink. There is also provided an organ fibrosis inhibitor comprising the active ingredients as described above either separately or as a combination of one of them with a mixture of the other two ingredients. Thus, it is possible to present organ fibrosis inhibitors such as a liver fibrosis inhibitor which are applicable in the form used in health foods for improving and maintaining liver function and foods and drinks for sick people, as well as drugs for various organ diseases caused by fibrosis such as liver diseases.