The objective of this study is to investigate the anticancer efficacy of a drug delivery system comprised of gelatin hydrogel (jelly) containing cisplatin (CDDP)-loaded gelatin/poly(acrylic acid) nanoparticles by peritumoral implantation and to compare the treatment response between the implantation administration of the jelly and intravenous (i.v.) administration of the nanoparticles. It is found that the implantation of the jelly containing CDDP-loaded nanoparticles on tumor tissue exhibited significantly superior efficacy in impeding tumor growth and prolonging the lifetime of mice than that of i.v. injection of CDDP-loaded nanoparticles in a murine hepatoma H(22) cancer model. An in vivo biodistribution assay performed on tumor-bearing mice demonstrated that the jelly implant caused much higher concentration and retention of CDDP in tumor and lower CDDP accumulation in nontarget organs than that of i.v. injected nanoparticles. Immunohistochemical analysis demonstrated that the nanoparticles from the jelly can be distributed in tumor tissue not only by their diffusion but also by the vasculature in the implantation region into tumor interior, enabling CDDP to efficiently reach more viable cells of tumor compared with i.v. injected nanoparticles. Thus, nanoparticles for peritumoral chemotherapy are promising for higher treatment efficacy due to increased tumor-to-normal organ drug uptake ratios and improved drug penetration in tumors.