YbMn0.17Si1.88 was synthesized from the reaction of ytterbium, manganese, and silicon using indium as a flux. The average structure of YbMn0.17Si1.88 was refined in the monoclinic space group P2(1), with a = 4.0107(8) angstrom, b = 3.8380(8) angstrom, c = 14.458(3) angstrom, beta = 97.97(3)degrees, R1/wR2 = 0.0296/0.0720. The structure can be described as the intergrowth of three AlB2-type layers and one E BaAl4-type layer. Magnetic susceptibility measurements suggest that the ytterbium atoms in,YbMnxSi2-x exist in a mixed valent or intermediate valent state. YbMn0.17Si1.88 shows weak antiferromagnetic ordering below similar to 4.5 K. The magnetic interactions between the Mn and Yb atoms in YbMn0.17Si1.88 are evident from the magnetic susceptibility measurements performed at low field. A negative magnetization is observed on warming and a positive magnetization on cooling. The heat capacity data suggest moderate heavy fermion behavior.