Background: Patients with Type 2 diabetes mellitus (T2DM) suffer cardiopulmonary impairment and may present with weakness of the inspiratory muscles. This study was designed to determine the effects of incentive spirometry (IS) on selected cardiopulmonary parameters, functional capacity and glycemic control in patients with T2DM. Methods: Fifty-nine participants (25 males and 34 females) recruited from the out-patient clinic of the Department of Medicine of two hospitals in Lagos State, Nigeria, who were randomly assigned into two groups, completed the study. In addition to the medical management of T2DM, IS group received incentive spirometry while control group continued with the medical management of T2DM alone. Selected cardiovascular parameters, pulmonary parameters, functional capacity (using 6-min walk test) and fasting blood glucose level were assessed at baseline and at the end of eight weeks intervention period. Data were analyzed using the Statistical Package for Social Sciences (SPSS Version 21). Level of significance was set at [Formula: see text]. Results: There were statistically significant improvements in all the cardiovascular parameters ([Formula: see text]) of IS group except systolic blood pressure. There were significant changes in all the pulmonary parameters, functional capacity and glycemic control ([Formula: see text]) of IS group while there was none in control group. There were significant differences between the mean changes of various selected outcome measures of the two groups ([Formula: see text]) except for diastolic blood pressure and blood glucose level. Conclusion: IS had positive effects in improving cardiopulmonary function, functional capacity and glycemic control in patients with T2DM.