We propose a way of measuring the photon polarization in radiative B decays into K resonance states decaying to Kππ, which can test the Standard Model and probe new physics. The photon polarization is shown to be measured by the up-down asymmetry of the photon direction relative to the Kππ decay plane in the K resonance rest frame. The integrated asymmetry in K1(1400) → Kππ, calculated to be 0.34 ± 0.05 in the Standard Model, is measurable at currently operating B factories.The Standard Model (SM) predicts that photons emitted in rare b → sγ decays are left-handed [1], up to small corrections of order m s /m b , while being righthanded inb →sγ. This feature is common to inclusive and exclusive radiative decays, also when including long-distance effects in the latter case [2]. While measurements of the inclusive rate agree reasonably well with SM calculations [1], no evidence exists for the helicity of the photons in these decays. In several models beyond the SM the photon in b → sγ acquires an appreciable right-handed component due to the exchange of a heavy fermion in the electroweak loop process. For instance, in SU (2) L × SU (2) R × U (1) left-right symmetric models [3] this component may be comparable in magnitude to the left-handed component, without affecting the SM prediction for the inclusive radiative decay rate. An independent measurement of the photon helicity is therefore of interest.Several strategies have been proposed to look for signals of physics beyond the SM through helicity effects in B → X s γ. In one method the photon helicity is probed through mixing-induced CP asymmetries [4]. In two other schemes one studies angular distributions in radiative decays of Λ b baryons [5,6] and in B → γ(→ e + e − )K * (→ Kπ) [7,8]. The methods using B mesons are sensitive to interference between amplitudes involving photons with left and right-handed polarization. In the SM the interference is at a level of a few percent, and these methods become unfeasible at present B factories also for larger interference due to insufficient luminosities. The methods using Λ b decays, measuring directly the photon polarization, rely on future hadron colliders or on extremely high luminosity e + e − Z factories.