Methotrexate is one of the anticancer drugs that can be safely administered subcutaneously, but locally injected MTX in aqueous solution form does not function in the administration site for very long. We developed a new dosage formulation: methotrexate bound to activated carbon particles (MTX-CH), and can report that it controlled tumor growth through its long-acting effect at the administration site. In this study, we investigated the effect of local administration of MTX-CH compared with MTX aqueous solution in tumors from transplanted human colon cancer cells (LoVo) into the back of nude mice. MTX-CH is superior to MTX aqueous solution in terms of its long-acting effect at the administration site and antitumor effect. We suggest that intratumoral injection therapy of MTX-CH is useful for patients in poor condition and with high surgical risk due to cardiac disease or old age, and patients who are diagnosed positive for cancer after endoscopic mucosal resection of early colorectal cancer.