The thermoluminescence (TL) glow peak height ratio of the main dosimetric peak (at about 240°C) and the lower temperature satellite peak (at about 140°C) of CaSO₄:Dy was found to vary between 1.4 and 11.5 in more than 100 batches of CaSO₄:Dy TLD tested in the last 5 years. Efforts were made to minimise the batch-to-batch variation. In most of the batches (90% of cases), the peak height ratio was more than 5 and the variation in the TL sensitivity (with respect to the reference batch) rarely exceeded 10%. The study of the grain size dependence of the peak height ratio of ground and unground and with and without acid wash of phosphor grains indicated that the surface effects contribute significantly to the batch-to-batch variation. Crystallisation of phosphor grains was found to be affected considerably by the interruptions in the process of evaporation of acid during the preparation. Phosphor grain size was found to be an important parameter for maintaining the quality of production of CaSO₄:Dy TLD phosphor.