The hydrolysis of mixed-metal cations (Al3+/CH3Sn3+) was studied in aqueous solutions of NaNO3, at I = 1.00 +/- 0.05 mol.dm(-3) and T = 298.15 K, by potentiometric technique. Several hydrolytic mixed species are formed in this mixed system, namely, Al-p(CH3Sn)(q)(OH), with (p, q, r) = (1, 1, 4), (1, 1, 5), (1, 1, 6), (2, 1, 4), (1, 2, 5), (1, 4, 11), (1, 3, 8), and (7, 6, 32). The stability of these species, expressed by the equilibrium: pAl(3+) + qCH(3)Sn(3+) + rOH(-) = Al-p(CH3Sn)(q)(OH)(r)(3(p+q)-r), beta(OH)(pqr) can be modeled by the empirical relationship: log beta(OH)(pqr) = -3.34 + 2.67p + 9.23(q + r). By using the equilibrium constant X-pgr relative to the formation reaction: pAl((p+q))(OH)(r) + q(CH3Sn)((p+q))(OH)(r) = (p + q)Al-p(CH3Sn)(q)(OH)(r), it was found that the formation of heterometal mixed species is thermodynamically favored, and the extra stability can be expressed as a function of the difference in the stability of parent homometal species. This leads, in turn, to a significant enhancement of hydrolysis and solubility.