Obesity results from fat accumulation in the body & results in multiple organ-specific pathological consequences. The prevalence of overweight and obese people is increasing worldwide at an alarming rate in both developing and developed countries. Weight reduction in obese patients is associated with an improvement of their health. This study aims to assessing the biochemical changes in the body of obese persons undergoing weight reduction program (WRP). The study was carried out on two groups, group I consists of (forty four (44) obese persons) with body mass index more than 30 undergoing WRP through diet and exercise & group II consists of (forty (40) obese persons not undergoing WRP as controls). The diet plan is the critical factor for weight loss, eating less & exercise more help to lose weight faster. Results of this study prove & magnify the beneficial value of WRP for obese persons in group I & explain its effects through the following: Significant reduction in body weight; Body Mass Index (BMI); Improvement (significant decrease) of: both systolic and diastolic blood pressure, blood glucose level, serum uric acid, serum creatinine, total serum cholesterol, LDLc & serum triglycerides; as well as significant increase of the protective lipid (HDLc). Also, there is improvement of liver function tests, i.e. significant decrease of liver enzymes (SGOT & SGPT) & significant increase of serum albumin. Overweight & obese persons should follow a program for weight reduction as early as possible & obese persons should investigate their biochemical changes regularly.