Background Mirabegron is a β3-adrenergic receptor (β3-AR) agonist indicated for the treatment of overactive bladder. β3-AR agonists are located in the urinary bladder and adipose tissue, where they are involved in the regulation of thermogenesis and lipolysis. Objective To evaluate the effect of mirabegron on lipid profile (serum cholesterol and triglyceride) and BMI in patients with OAB. Materials and Methods In the medical city complex (Ghazi AL-Hariri Hospital) urology outpatient clinic, a prospective study of 40 patients diagnosed with OAB. These patients took a single dose of mirabegron 50 mg for 4 months and assessed its effect during this period on weight and fasting serum (s.) cholesterol and triglycerides. Results Investigation showed that there is a statistically significant reduction from baseline after 2 and 4 months of treatment with mirabegron (P-value = 0.001) in fasting s. Triglyceride, while fasting s. cholesterol level showed an increase in level after 2 and 4 months of treatment. However, this increment not statically significant after 2 months (P-value = 0.227) and after 4 months (P-value = 0.261) BMI showed slightly reduction after 2 and 4 months’ treatment with mirabegron but also this reduction not statically significant after 2 months (P-value = 0.114) and after 4 months (P-value = 0.562). Conclusion Mirabegron causes an interesting and useful decline in the level of triglyceride, which is responsible for cardiovascular disease.