The crystal structure of YAl3C3 was refined from laboratory X-ray powder diffraction data (CuK alpha(1)) using the Rietveld method. The crystal structure is hexagonal (space group P6(3)mc, Z=2) with lattice dimensions a=0.342157(4) nm, c=1.72820(1) nm, and V=0.175217(3) nm(3). The final reliability indices were R-wp=9.94% (R-wp/R-e=1.18), R-p=7.36%, R-B=1.77%, and R-F=1.03%. The compound shows an inter-growth structure with electroconductive [YC2] thin slabs separated by Al4C3-type [AlC] layers. This material had thermoelectric properties superior to those of the layered carbides Zr-2[Al3.56Si0.44]C-5, Zr2Al3C4, and Zr3Al3C5 in the temperature range of 500- 1073 K, with a maximal power-factor value of 1.96 x 10(-4) W center dot(m center dot K-2)(-1) at 1073 K.