Physical activity levels were measured in obese and non-obese 8- to 12- year-old schoolboys (n=296). Anthropometric measures included weight, height, body mass index (BMI), triceps and subscapular skinfolds, predicted fat percentage, fat mass (FM), fat-free mass (FFM), FM index (FMI), and FFM index (FFMI). Physical activity was assessed using an electronic pedometer for three continuous weekdays. Boys were divided into active and inactive groups based on daily accumulation of pedometer counts above or below 13,000 steps. Obesity was defined as body fat content that equals or exceeds 25% of body weight. The international age- and gender-specific child BMI cut-off points were also used to define overweight and obesity. Estimated fat content for the whole sample averaged 23.3±9.7%. More than 37% of the boys were classified as obese. The mean step counts were about 13,489±5,791 steps per day (range: 335–29,169 steps). Over 71% of the boys accumulated 10,000 steps or more per day. Based on BMI standards, mean step counts for the obese group (10,602±4,800 steps/day) were significantly (p=0.004) lower than in the normal group (14,271±5,576 steps/day). Based on fat percentage, obese boys also accumulated significantly (p=0.009) lower numbers of steps per day (12,682±5,236) than did non-obese boys (14,915±5,643). Further, there were significant differences (p<0.05) between active and inactive boys in weight, BMI, triceps and subscapular skinfolds, fat percentage, FMI, and flexibility. It is concluded that the prevalence of obesity and inactivity among Saudi boys aged 8–12 years was high. Active boys exhibited significantly lower body fat percentage and BMI than inactive peers. Obese boys, on the other hand, were significantly less active than non-obese boys. Increased prevalence of obesity and physical inactivity among Saudi children is a major public health concern.