Barium titanate powders with average crystallite sizes of 68-2000 nm have been prepared by the calcination of barium titanyl oxalate (BTO) at temperatures of 700-1150 degrees C. The morphology and recrystallization kinetics of the powders have been studied using the SEM and X-ray methods. Samples of PTCR (BaCaPb)TiO3 ceramics have been made from these powders and their microstructure and electrical properties have been investigated. It has been found that the increase of the crystallinity of the starting powders suppresses recrystallization of the ceramics, leading to growth in resistivity and significantly influencing on the resistance jump and breakdown strength of the ceramics. An optimal temperature range for the calcination of BTO has been found to ensure maximum breakdown strength of the PTC thermistors with the resistance of 31 Omega. At this temperature range the barium titanate powders had crystallite sizes of similar to 200 nm.