A quasi-experimental study to assess the effectiveness of box-breathing on pain among post operative patients in selected hospitals of Gandhinagar. The study was conducted among post operative patients in selected areas of Gandhinagar. The main aim of the study is to evaluate the effectiveness of box breathing on pain among post-operative patients in selected hospitals of Gandhinagar. The general system model was used as conceptual framework. A quantitative approach with quasi experimental study design was used to achieve the objective of the study. The result shows that box breathing given to the post-operative patients in experimental group, the level of pain was minimized which was assessed by standardized numerical pain rating scale. In experimental group the pre-test mean is 6.08 and the post-test mean is 3, the mean difference was 3.08, standard deviation of pretest was 1.25 and of posttest was 1.38 which showing that level of pain was minimized. In control group, the pretest mean is 6.24 and the posttest is 4.96, the mean difference is 1.28, standard deviation of pretest is 1.45 and of posttest is 1.81. Calculated t value is 5.51 which is more than table value at 0.05 level of significance. So null hypothesis is rejected and research hypothesis is accepted which showing effectiveness of box breathing exercise. This study therefore, offers an encouraging solution towards improvement of post operative patients condition and change in pain score after providing box breathing exercise. The study intends to assess the effectiveness of box breathing on pain among post operative patients in selected hospitals of Gandhinagar. The study reveals that the post test pain score is lower than the pretest pain score.