We consider the Pohlmeyer-reduced formulation of the AdS5 ×S 5 superstring. It is constructed by introducing new variables which are algebraically related to supercoset current components so that the Virasoro conditions are automatically solved. The reduced theory is a gauged WZW model supplemented with an integrable potential and fermionic terms that ensure its UV finiteness. The original superstring theory and its reduced counterpart are closely related at the classical level, and we conjecture that they remain related at the quantum level as well, in the sense that their quantum partition functions evaluated on respective classical solutions are equal. We provide evidence for the validity of this conjecture at the one-loop level, i.e. at the first non-trivial order of the semiclassical expansion near several classes of classical solutions. 1 benjamin.hoare08@imperial.ac.uk 2 yukinori.iwashita07@imperial.ac.uk 3 Also at Lebedev Institute, Moscow. tseytlin@imperial.ac.uk P SU(2, 2 | 4) Sp(2, 2)×Sp(4) supercoset, which may be written in terms of the P SU (2, 2 | 4) current one may solve the Virasoro conditions by introducing the new variables g ∈ G = Sp(2, 2) × Sp(4), A ± ∈ h, 1 and Ψ L,R , which are algebraically related to the current components. The resulting equations can then be obtained from a local action I red (g, A ± , Ψ L,R ) which happens to be the G/H gauged WZW model modified by an H-invariant potential and supplemented by the 2-d fermionic terms (see [1] and (2.24),(2.25) below). This action, which defines the reduced theory, is 2-d Lorentz invariant and (after fixing the residual H gauge symmetry) involves only the physical number (8+8) of bosonic and fermionic degrees of freedom.The original AdS 5 × S 5 superstring theory and the reduced theory are essentially equivalent at the classical level, having closely related integrable structures and sets of classical solutions. The question that we would like to address here is if this correspondence may extend to the quantum level.Since the classical Pohlmeyer reduction utilizes conformal invariance, it has a chance to apply at the quantum level only if the sigma model one starts with is UV finite. This is the case for the AdS 5 × S 5 superstring sigma model, [19,20,21,22], which is a combination of the AdS 5 and the S 5 sigma models "glued" together by the Green-Schwarz fermions into a conformal 2-d theory. For consistency, the corresponding reduced theory, [1,2], should also be UV finite. That was indeed shown to be true to the two loop orders and is expected to be true also to all orders, [4].It should be emphasized that we are interested in the reduced theory only as a tool for describing observables of the original string theory: it is the string theory that should dictate those quantities one should compute in the reduced theory. 2We start with the 2-d worldsheet sigma model arising from the Green-Schwarz action for the Type IIB superstring theory on AdS 5 × S 5 after fixing the conformal gauge. This is the F/G coset sigma model where F = P SU (2,...