To evaluate the effect of tranilast eyedrops in preventing fibrous opacification of the posterior lens capsule after cataract extraction and intraocular lens (IOL) implantation. The Second Department of Ophthalmology, Toho University School of Medicine, Tokyo, and Shohzankai Medical Foundation, Miyake Eye Hospital, Nagoya, Japan. This study comprised eyes having continuous curvilinear capsulorhexis and phacoemulsification/aspiration followed by implantation of a posterior chamber IOL in the capsular bag. In this prospective, randomized, controlled, and double-masked trial, tranilast 0.5% (Rizaben) eyedrops (15 eyes) or its placebo eyedrops (20 eyes) were given 4 times a day for 3 months after surgery. An anterior eye segment analysis system (EAS 1000, Nidek Co., Ltd.) was used to evaluate the degree of fibrous posterior capsule opacification (PCO) 1 week and 1 and 3 months after surgery. The mean PCO density in the tranilast group was 17.1 cct +/- 4.6 (SD), 20.0 +/- 3.6 cct, and 23.0 +/- 7.7 cct (cct = computer compatible tape) at 1 week and 1 and 3 months, respectively. In the control group, it was 18.2 +/- 5.3, 30.2 +/- 7.8, and 38.4 +/- 8.0 cct, respectively. There was a significant difference in the 1 and 3 month findings between the 2 groups (P < .001). Tranilast was effective in preventing fibrous PCO at an early postoperative stage. The possible mechanisms of its effect may be prevention of collagen synthesis by minimizing transforming growth factor type beta released during lens epithelial cell metaplasia.