Background: To improve the speed and efficiency of root canal therapy, stainless steel instruments have been Abstract used in a variety of preparation techniques, in an attempt to produce the appropriate canal shape. However, studies have shown that procedural incidents occur commonly, producing aberrations such as formation of hourglass-shaped canals, zips, elbows and canal transportation. Nickel-Titanium (NiTi) rotary instruments are thought to reduce such aberrations. Hence; we undertook the present study to assess and compare the efficacy of engine-driven method (Ni Ti Rotary) and conventional manual methods with stainless steel K-files in performing root canal therapy in permanent molars.Materials & methods: The present study included assessment of efficacy of engine-driven method (Ni Ti Rotary) and conventional manual methods with stainless steel K- files in performing root canal therapy in permanent molars. 50 extracted teeth were randomly divided into two study groups as follows: Group I: Teeth in which Conventional stainless steel instruments were used, Group II: Teeth in which NiTi rotary instruments were used. Root canal therapy was performed in both the study groups by same experienced and endodontist. All the results were analysed by SPSS software. Results: Time of preparation in teeth of group I and group II was 9.36 and 14.62 minute respectively. Significant results were obtained while comparing the mean preparation time in both the study groups. Conclusion: Rotary instruments are less time consuming and increase the efficacy of the operator in performing root canal therapy. Key words: Root canal therapy, Rotary, Stainless steel