Mixed-metal oxides with the composition Y
3
Sc
x
Ga
5-x
O
12
(x = 2.0, 2.1, 2.2, 2.25, 2.3, 2.4, 2.5, and 3.0) have been prepared by an aqueous sol-gel method. The effects of scandium substitution on the garnet phase formation were studied by IR spectroscopy and X-ray powder diffraction (XRD). The XRD data indicate that single-phase Y
3
Sc
x
Ga
5-x
O
12
ceramic samples were obtained for x = 2.0, 2.1, 2.2, 2.25, 2.3, and 2.4. The results also show that the formation of Y
3
Sc
x
Ga
5-x
O
12
garnets depends on the molar ratio of scandium and gallium in the investigated composition, and consequently on the mean cationic radius at the Al
3+
sites. The variation of lattice parameters for the Y
3
Sc
x
Ga
5-x
O
12
phases with different x is reported.