To determine the efficacy of instillation frequency and submucosal injection of platelet-rich plasma (PRP) after urethral trauma to prevent urethral inflammation and spongiofibrosis. Sixty-five rats were used in the study; 50 rats were randomized into 5 groups with 10 rats in each group and 15 rats were allocated for PRP preparation. The urethras of all rats were traumatized with a pediatric urethrotome knife at 6 and 12 o'clock positions, except in the sham group. Group 1 was the sham group and had only urethral catheterization daily for 15 days, Group 2 was given 0.9% saline (physiologic saline [(UI+PS]) once a day after urethral injury (UI+ PS), Group 3 was injected with PRP submucosally after urethral injury, Group 4 was given PRP once a day as intraurethral instillation using a 22 Ga catheter sheath with urethral injury, and Group 5 was given PRP twice a day as intraurethral instillation using a 22 Ga catheter sheath with urethral injury. Each administration of PRP was administered as 300 million platelets/150 microliters. On day 15, the penises of the rats were degloved to perform penectomy. Histopathologic evaluation was made for spongiofibrosis, inflammation, and congestion in vascular structures. When the sham group, UI+PS, UI+PRPx1, UI+PRPx2 and UI+PRPs groups are compared in total, there were significant differences identified for parameters other than edema. When the UI+PS, UI+PRPx1, UI+PRPx2 and UI+PRPs groups are compared, the UI+PS group was observed to have significantly more inflammation (mucosal inf. 2.42 ± 0.53) and spongiofibrosis (2.42 ± 0.53). All the PRP groups were identified to have significantly less mucosal inflammation (UI+PRPs 1 ± 0, UI + PRPx1; 1.4 ± 0.51, PRPx2; 1.33 ± 0.5) and spongiofibrosis (UI+PRPs; 1.57 ± 0.53, PRPx1; 1.2 ± 0.42, PRPx2; 1.55 ± 0.52). The group with the lowest spongiofibrosis was the PRPx1 group. This study showed that PRP significantly reduced mucosal inflammation and spongiofibrosis, independent of the administration route, when applied to the urethra after urethral trauma.