A study of the dielectric properties of the lanthanum doped Sr0.3Ba0.7Nb2O6 (SBN30) ceramic according to the stoichiometric formulation Sr0.3-3y/2LayBa0.7Nb2O6 with y = 0.01, 0.03 and 0.05, and the influenceof the sintering conditions are reported. The XRD shows single phase compoundsfor Sr0.285La0.01Ba0.07 Nb2O6(LSBN1) and Sr0.255La0.03Ba0.7 Nb2O6(LSBN3) ceramics, both samples having similar microstructure, densificationand dielectric properties. The density increases linearly with Lnt, wheret is the sintering time, and the values of the maximum ferroelectric peaksof the permitivity rise steadily with t. Using the Bruggeman model to estimatethe theoretical permitivity, it is concluded that the magnitude of theexperimental permitivity peaks are mainly affected by the volume fractionof porosity of the samples. In this study we also establish that poresdiffusion mechanisms behave according to the Ginstling-Brownshten equation.For Sr0.225La0.05Ba0.7 Nb2O6(LSBN5) sample, XRD analysis reveals the presence of isostructural compoundsof the intermediate phases BaNb2O6 and SrNB2O6,and the dielectric properties start to deteriorate. This fact indicatesthe existence of a solubility limit of the Lanthanum ions in the SBN solidsolution-