Aim: to compare between the prevalence of obstetric anal sphincter injury (OASIS) after cutting mediolareral episiotomy by angled, curved or straight scissors in women in labour. Methods: The current randomized controlled trial was conducted at Ain Shams University Maternity Hospital. The participating women were randomly allocated into three arms. Arm (A): women had mediolateral episiotomy cut by angled scissors. Arm (c): women had mediolateral episiotomy cut by curved scissors .Arm (s): women had mediolateral episiotomy cut by straight scissors. Primary outcome was the occurrence of Obstetric Anal Sphincter Injuries (OASIS). Results A total of 300 primiparous women were included. The overall incidence of OASIS was 5%,17% and 15 % in arm A,C and S respectively. Conclusion: using angled scissors in cutting mediolateral episiotomy results in less cases of obstetric anal sphincter injury compared to cutting episiotomy by straight or curved scissors.