Technological applications of single crystal MCT with x = 0.2 for infrared detectors require improved electrical parameters which are closely related to the presence of defects (dislocations, subgrains, precipitates). The authors have already established that edge dislocations were arranged forming mostly tilt-type sub-boundaries (1). In this paper, subgrain (SG) growth on thermal annealing (30-60 days at 650 degrees C) was studied by X-ray topography. Results were evaluated statistically, and SG size was found to be Log-normal distributed. Some remarks on the slight growth in SG size are given.