Introduction: Anal fissure is a common proctological problem which presents with pain in the anal region during and after defecation. An idiopathic chronic anal fissure is one of the most common and important lesions of anal canal encountered in surgical practice. Open and Closed lateral internal sphincterotomy (OLIS and CLIS) are the two surgical techniques used to treat fissure in Ano. Objectives: To compare post operative complications and pain after performing either of the two surgical procedures (Open and Closed lateral internal sphincterotomy) for the treatment of fissure in Ano. Methodology: A Prospective study was conducted for a duration of 11 months in a medical college hospital of Hubli, Karnataka among 59 patients who were diagnosed with fissure in Ano, who were randomly allocated to either of the two treatment groups (A or B). Participants in Group A underwent closed Lateral Internal Sphincterotomy and group B patients underwent Open Lateral Internal Sphincterotomy. They were followed up for 3months for post operative complications, The pain was analysed using Visual Analog scale (VAS). Results: Chronic fissure in Ano was commonly seen in the middle age group with the mean age of presentation of 35.69 ± 13.21 years. 78% of patients had pain during defecation and bleeding PR as their chief complaints. 12 patients (20%) had postoperative complications in OLIS group and 6 patients (20.7%) developed postoperative complications in CLIS group. Postoperative pain was significantly less in CLIS group than in OLIS group. Conclusion: It can be concluded by the research that (CLIS) closed lateral internal anal sphincterotomy is a better choice to treat chronic fissure in Ano than OLIS which can be done effectively and safely with acceptable complication rate and excellent results.