Polycrystalline yttrium lanthanum iron garnets (Y3La (x) Fe5-x O-12) with varying La substitution (0 <= x <= 0.5) have been prepared in the pellet form, and studied by X-ray diffraction, magnetization, a.c. susceptibility and electrical resistivity measurements. The lattice constants are determined and the applicability of Vegard's law has been tested. The saturation magnetization (4 pi M-S) decreases very slowly almost linearly with increasing x from x = 0.0-0.5 indicating minimal reduction in ferrimagnetism and least magnetic loss. Variation of saturation magnetic moment per formula unit at 300 K with x can be explained satisfactorily assuming the collinear spin-ordering model. The Curie temperature (T-c) reduces very slowly with increasing x, which is consistent with the observed decrease in 4 pi M (S) with x. The activation energy (E) decreases very slowly with increasing x for x > 0.1.