The aim of this study was to investigate the immunosuppressive activity of a mycophenolate mofetil (MMF) intraocular-implantable drug delivery system (IDDS) in a rabbit model of high-risk penetrating keratoplasty and to determine the biocompatibility of such a device when implanted in the anterior chamber. Corneal vascularization was induced in New Zealand white rabbits by passing 5-0 silk sutures through the corneal stroma in each quadrant. The corneal neovascularized rabbits received a unilateral 7-mm-diameter central-penetrating keratoplasty. New Zealand white rabbits were used as donors and were divided into 4 treatment groups: the control group, which received no therapy; the 1% MMF eye drop group; the 1.0 mg cyclosporin A (CsA)-IDDS-implanted group; and the 1.0 mg MMF-IDDS-implanted group. Animals were followed up for 150 days, which involved examination of the corneal allografts (opacity, edema, and neovascularization) by slit-lamp biomicroscopy. The survival time of corneal allografts of these animal models was recorded in 4 groups. Histopathologic studies were carried out on the procured specimens of corneal allografts. The biocompatibility of MMF-IDDS in the anterior chamber in rabbits was also investigated. The mean survival time of corneal allografts in the control and MMF eye drop groups was 18.7±3.0 and 37.5±6.2 days, respectively (P=0.005). Allografts from the CsA-IDDS-implanted group were transparent, except 1 allograft, which showed immune rejection after 130 days. Allografts from the MMF-IDDS-implanted group were transparent throughout the entire observation period. The incidence of allograft rejection was 100% in the control and MMF eye drop groups, respectively. The rejected allografts were much more edematous and more heavily infiltrated with leukocytes than the nonrejected allografts. MMF-IDDS was tolerated well in the anterior chamber, even with 3 MMF-IDDS implanted in the anterior chamber at 1 time. MMF-IDDS was able to prolong high-risk allograft survival time and significantly inhibited corneal immune rejection in the rabbit model of penetrating keratoplasty. The device could safely be implanted in the anterior chamber without adverse effects.