Objectives: Peritoneal fibrosis (PF) results in ultrafiltration failure in peritoneal dialysis (PD) patients. Peritoneal Myofibroblasts (PMFBs) characterized by increased alpha-smooth muscle actin (α-SMA) expression, extracellular matrix (ECM) proteins production are key cells in the pathogenesis of PF. 5-hydroxytryptamine (5-HT; serotonin) induces ECM synthesis in fibroblasts in a transforming growth factor beta 1 (TGF-β1) dependent manner.   Methods: Biopsy from parietal peritoneum (PB) of control patients (n=8) and PD patients (n=6) excised during laparotomy was incubated overnight in dispase (2.4 U/mL)/37°C. Human peritoneal fibroblasts (HPFBs) obtained, were incubated with TGF-β1 (10ng/ml) for 1 hour and later with TGF-β1 (10ng/ml)/ [Sildenafil (10µM) or SB204741 (1µM)] and their combination for 24 hours (Post-treatment strategy). In pre-treatment strategy, HPFBs were pre-treated with [Sildenafil (10µM) or SB204741 (1µM)] and combination of the two for 1 hour and later with only TGF-β1 (10ng/ml) for 24 hours. Real time PCR for pro-fibrotic (COL1A1, COL1A2, ACTA2, CTGF ,FN1, TGFΒ1) and anti-fibrotic genes (MMP2/TIMP1) expression was performed. Levels of cytokines IFN-g, IL-4, IL-17, IL-1β, IL-6, TNF-a (proinflammatory) and IL-10 (anti-inflammatory) in culture supernatant of HPFBs were determined by ELISA. Results: In this study, anti-fibrotic effect of combination of Sildenafil and SB204741 was greater than that of each drug alone. In TGF-β1 stimulated HPFBs, upregulated expression of pro-fibrotic genes was observed (p<0.05). Expression of pro-fibrotic genes reduced significantly (p<0.05) with almost complete amelioration of ACTA2 (figure 2). Ratio of anti-fibrotic genes (MMP2/TIMP1) was restored (p<0.05) (figure 3). Production of proinflammatory cytokines also reduced (p<0.05) with increase in IL-10 levels (p<0.05). Conclusions: This study suggests that the combination of Sildenafil and SB204741 may be efficacious in treating PF in its active phase.