The oscillating magnetocaloric effect in a size-quantized diamagnetic film in a transverse magnetic field has been considered. Expressions for the thermodynamic potential and entropy have been derived. It has been shown that a change in entropy is an oscillating function of the magnetic field. The nature of this effect is the same as of the de Haas–van Alphen effect. It has also been shown that a change in entropy is an oscillating function of the film thickness. Comparison with 3D and 2D systems has been performed. Qualitative interpretation of the results has been presented.