  We investigate the twist-3 pion and kaon distribution amplitudes of the
pseudoscalar (phi^p_{pi,K}) and pseudotensor (phi^{sigma}_{pi,K}) types, based
on the effective chiral action from the instanton vacuum. Effects of flavor
SU(3) symmetry breaking are explicitly taken into account. The Gegenbauer
moments and the moments of the distribution amplitudes (<xi^m>) are also
computed. Our results are summarized as follows: a^p_{2,pi} ~ 0.4, a^p_{1,K} ~
0.02 and a^p_{2,K} ~ 0.14, and a^{sigma}_{2,pi} ~ 0.02 and a^{sigma}_{1,K} ~
a^{sigma}_{2,K} ~ 0; <xi^2>^p_{\pi} ~ <xi^2>^p_K ~ 0.37 and <xi>^p_K ~ 0, and
<xi^2>^{sigma}_{pi} ~ <xi^2>^{sigma}_K ~ 0.20 and <xi>^{sigma}_K ~ 0. We
compare our results with those from the QCD sum rules. We also discuss the
relevant Wilson coefficients which were analyzed recently in chiral
perturbation theory.
