The grain growth mechanisms along the BaTiO3 fibers were studied between 1150 degrees C and 1250 degrees C. The normal grain growth always reached a stagnant stage after certain heat-treatment duration caused by the surface pinning effect. However, the abnormal grain growth (AGG) was not pinned by such surface effect, and can grow continuously. The confined normal grain (or matrix grain) size provides the driving force for AGG. The fiber diameter has an important influence on the grain growth behaviors. Submicrometer fibers have relative small stagnant grain sizes, resulting in large driving force for AGG. Abnormal grain growth occurred below 1200 degrees C in the submicrometer diameter fibers, but was not observed at the same temperature in the fibers with diameter of above 1m. Due to the large AGG driving force, large number densities of abnormal grains were observed in submicrometer fibers, resulting in bamboo-like microstructure. Fibers with diameters of 1-2m were able to be converted into single crystal fibers up to several tens of micrometers due to the relative small AGG driving forces.