Study of the dielectric tunability and susceptibility, in a wide temperature range and at different bias fields, in BaSr TiO (BST) sol-gel derived ceramics of different crystallite sizes (between 1 and 6 μm), establishes two new regularities. The first one concerns the relative temperature of the maxima positions of the tunability and susceptibility. We show that the maximum in tunability is always at lower temperatures compared to the maximum in susceptibility. The second regularity tells that the electric field dependence of the susceptibility maximum temperature is always stronger than the one for the tunability maximum temperature. In small-size crystallite BST ceramics the temperature of susceptibility maximum starts changing only above a certain threshold field. Additionally, we discuss the nature of an extrinsic contribution to tunability in small-size crystallite BST ceramics. © 2011 Elsevier B.V. All rights reserved.