The polarization properties of InGaN quantum wells on nonpolar AlInGaN alloy substrates are calculated numerically using the 6×6 k·p Hamiltonian. It is shown that the polarization direction of quantum‐well emission changes, depending on the substrate alloy composition and quantum well width, and that these polarization switches are caused by the strain anisotropy and quantum confinement effects in the quantum wells. The calculations indicate that the utilization of InGaN or AlInGaN alloy substrates can be beneficial in obtaining desirable polarization properties for the formation of cleaved‐facet cavity mirrors in laser diodes on nonpolar substrates. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)