Background: In incisional hernia patients, collagen type I/III ratio and total collagen density (TCD) emerges a main etiological factor. If they are low, recurrence risk can be high. The aim of this study was to determine the ratio of collagen type I/III and TCD after incisional hernia repair in different layers with polypropylene mesh.Methods: In the study, 40 Wistar Albino rats were used. They were divided into four equal groups: control, preperitoneal, intraperitoneal and onlay. In control group, defect was repaired with prolene suture. In other groups, prolene mesh was placed to the different layers. Incisions were reopened 30 days later, and tissue samples were taken. Samples were stained by double-immunohistochemical methods and examined under light microscope.Results: Collagen type I/III ratio and TCD was highest in preperitoneal group. Intraperitoneal group was the second highest group. There was no difference between onlay and control group for collagen type I/III ratio except TCD. There was a significant correlation between TCD and collagen type I/III ratio in all samples.Conclusions: Mesh repair in different layers has an effect on TCD and collagen type I/III ratio in incisional hernia repair. Preperitoneal layer is better than other layers.