An experimental study to investigate the effect of the particle size (d) andReynolds number (Re) for different values of heat flux on the heat transfer coefficient(h) in gas-solid fluidized bed was done. In this work three different sizes of sand particles were employed (525,725 and 925mµ ). The fluidizing medium was air at different velocities in the range of (1.9-2.9 m/s). The rig provided with a horizontal heating tube with outer diameter of (3.175cm) was heated eclectically with different power supplies (69,90,120 and 150 W) . The fluidized bed temperature profiles were evaluated axially in the fluidized bedfor different positions. The recording and the monitoring of these measurements weredone by an interface system connected with PC computer. The results show that the temperature distribution decreases with increase particlesize and the heat flux represents as the temperature increases as the air velocitiesincrease . A new empirical correlation was suggested in this study .The correlation predicts the value of (Nup) as a function of both (Rep) and (Fr). All the dimensionlessgroups are determined based on particle diameter . 48.057.0Re0042.023.5Re0738.0ppp+=pp<<<<1675406168Re61FrFrNu ppp