We have measured the static dipole polarizability of Na(y-x)Li(x) clusters (with y=2, 3, 4, and 8) by molecular beam deflection technique. For a given size, the polarizability of pure lithium clusters is smaller than the polarizability of pure sodium clusters. For mixed clusters, a smooth decrease in the polarizability is observed as the proportion of lithium atoms increases. For the NaLi molecule, both experimental permanent dipole and average polarizability have been obtained. Experimental results are compared to results of density functional theory and configuration interaction single and double (CISD) ab initio calculations. (C) 1999 American Institute of Physics. [S0021-9606(99)01512-3].