The structural and magnetic properties of Nd2AlFe16−xMnx (x = 1, 2, 3, 4, and 5) compounds have been investigated by means of X-ray diffraction and magnetization measurements. The Nd2AlFe16−xMnx compounds have a rhomhedral Th2Zn17-type structure. There exist an anisotropic strong spontaneous magnetostriction in magnetic state and a negative thermal expansion near their Curie temperatures. The nearly zero thermal expansion coefficient is found over a broad temperature range including room temperature from 103 to 342 K for Nd2AlFe15Mn compound. In the magnetic state, the thermal expansion coefficients of Nd2AlFe16−xMnx compounds increase with the increasing Mn concentrations x. Mn concentration dependences of the lattice parameters and unit-cell volume, the spontaneous magnetostrictive deformation, the Curie temperature, and the saturation magnetization have been discussed.