The purpose of the present study was to examine of the effects of upper body kinematics on the ball velocity at the impact phase of a tennis flat serve. 15 elite male tennis players were recruited to participate in this study (mean age 18.4 +/- 3.3 years, mean height 182.3 +/- 5.6cm, mean weight 72.2 +/- 7.9kg), of which five were from the Turkish National Team. Players performed flat tennis serves on a regulation indoor tennis court. Data were recorded digitally to computer hard drives on court using three Basler A602f cameras at 100Hz. The Radar gun (Sports Radar, Astro Products, CA), was used for velocity measurements of the tennis balls. The Spearman Rank Correlation procedure was used to determine the relationships between parameters and balls. Relationships between elbow angular velocity and trunk angular velocity, as well as between elbow angular velocity and wrist angular velocity were found. The ground reaction forces transmitted through the legs and trunk allowed for greater angular velocity of the elbow, which in turn provided a favourable advantage by affecting the wrist speed and ultimately, the ball speed.