The static dipole polarizabilities of two-electron systems confined by a spherical harmonic-oscillator potential ! have been calculated by the coupled-cluster CCSD method. The combined effect of the confining potential ! and the central electrostatic field on the polarizabilities of the quantum dot, and the confined systems, H À , He and Li þ , respectively, have been investigated. The polarizabilities of the quantum dot can be calculated analytically. The polarizability of the 2-electron quantum dot for ! ¼ 0.01 is calculated to be 19 996 au, in perfect agreement with the exact value, 20 000 au. Already medium confinement, ! ¼ 1.0, reduces to 2.00 au. The decrease of the polarizability is smaller for H À ( ¼ 216:1 au for ! ¼ 0.0 and 0.985 au for ! ¼ 1.0), and much smaller for He and Li þ (1.3819 and 0.3813 au for He for ! ¼ 0.0 and ! ¼ 1.0, respectively, and 0.1921 and 0.128 au for Li þ ). The theoretical polarizabilities for unconfined (! ¼ 0.0) H À , He and the Li þ cation are in very good agreement with the best published theoretical and/or experimental data. Our final polarizability for H À , 216:0 AE 0:5 au, appears to be one of the most accurate values published so far. The optimization procedures of basis sets applicable to calculations of polarizabilities of systems confined by a spherical harmonic-oscillator potential are presented.