This paper presents the experimental and numerical evaluations of the ac loss characteristics of one- and two-layer polygonal conductors assembled by YBCO tapes. The ac losses in the one-layer pentagonal and hexagonal conductors with various tape-to-tape gaps are measured, and the numerical simulation of the ac losses in the test conductors is performed by a previously developed numerical model. It is shown that the measured dependence of the ac loss in the one-layer polygonal conductors on the tape-to-tape gap is explained well by the numerical model. In the two-layer hexagonal conductor, the numerical simulation results also are in good agreement with the measurement results. It is considered that the experimental and numerical results obtained in this study support the validity of our previous studies on the ac loss in the polygonal assembled conductors made of thin high-temperature superconducting tapes. © 2002-2011 IEEE.