We explore the possibility for an evaluation of non-leptonic DeltaS = 1 K decay amplitudes through the calculation of K --> pi matrix elements using domain-wall QCD. The relation between the physical K --> pi pi matrix elements and K --> pi matrix elements deduced from chiral perturbation theory is recapitulated. Quenched numerical simulations are performed on an 16(3) x 32 x 16 lattice at a lattice spacing a(-1) approximate to 2GeV for both the standard plaquette gauge action and a renormalization-group improved gauge action, and reasonable signals for K --> pi matrix elements are obtained. Preliminary results are reported on the K --> pi pi matrix elements, and results from two actions are compared.