We evaluate the a_1(1260) rightarrow pi sigma (f_0(500)) decay width from the perspective that the a_1(1260) resonance is dynamically generated from the pseudoscalar–vector interaction and the sigma arises from the pseudoscalar–pseudoscalar interaction. A triangle mechanism with a_1(1260) rightarrow rho pi followed by rho rightarrow pi pi and a fusion of two pions within the loop to produce the sigma provides the mechanism for this decay under these assumptions for the nature of the two resonances. We obtain widths of the order of 13–22 MeV. Present experimental results differ substantially from each other, suggesting that extra efforts should be devoted to the precise extraction of this important partial decay width, which should provide valuable information on the nature of the axial vector and scalar meson resonances and help clarify the role of the pi sigma channel in recent lattice QCD calculations of the a_1.