Rotary kilns are gas-solid reactors commonly used in industry to achieve a wide array of material processing operations. Rotary kilns are used for applications such as reduction of oxide ore, pyrolysis of hazardous waste, calcining of petroleum coke, conversion of uranium fluoride into uranium dioxide for the manufacture of nuclear fuel, and so on. When operated at atmospheric pressure, they consist of a cylindrical shell that can be inclined, into which the solid charge is fed continuously at one end and discharged at the other. They can be equipped with lifting flights or lifters, and/or dam(s) at the kiln end(s). They are classified into two main heating modes: either directly heated or indirectly heated, depending on the heating source location with respect to the solid material. They usually require very little labor to operate. Heat transfer in rotary kilns is very complex and may involve the exchange of energy via all the fundamental physical transfer mechanisms that are, conduction, convection, and radiation. There has been a significant amount of studies dealing with this subject in the literature. Although many researchers studied the main phenomena occurring in the kiln, the heat transfer between the wall and particles is not yet well understood. Therefore, this study aimed at determining the wall-to-solids heat transfer coefficient. The effects of various operational parameters such as the filling degree, the rotational speed, lifters profile as well as the temperature set point at the outer wall on the mentioned heat transfer coefficient are also analyzed in this study. A series of experiments were carried out on a pilot scale rotary kiln at atmospheric pressure, whether or not equipped with lifters and fitted with dam at the outlet end. The experimental rotary kiln is externally heated by electrical resistance and equipped with thermocouples positioned at five cross-sections, in and outside along the kiln tube. These experiments aimed at recording the heating up of the wall, gas and solid particles after turning on the heating system until temperatures are stabilized; the afore-mentioned coefficient was determined from the temperature profiles measurements data for low and medium wall temperature set point. The bulk materials used was quartz sand (average size 0.55 mm) with a narrow distributed size fraction. Furthermore, two shapes of lifters were compared to determine the influence of lifter and their geometry: straight lifters (SL) and rectangular lifters (RL). The other operational parameters mentioned were also varied so that a matrix of about 60 experiments (without including repeatability tests) was achieved. The solids temperature fluctuations after the start of the heating system can be considered as response of a first-order system, therefore characterized by a time constant. Results show that the time constant decrease with the temperature set point at the outer wall and the filling degree, but increase in presence of lifters. However for the two types of lifters used, the time constant remains of the same order of magnitude. Calculation of the heat transfer coefficient has been done from the overall heat balance ODE, its analytical solution and the time constant. The third method of calculation give results an order of magnitude greater than the first two but follow similar tendency. The heat transfer coefficient from wall to solids seems to decrease in presence of lifters and increase with the filling degree. The heat transfer coefficient also increases with the temperature set point at the outer wall as well as the rotational speed (for a constant filling degree).