The solubility of manganese ion in layered perovskite La4Ni3O10 phase was examined and the detailed crystal structure of this phase was discussed. The solid solution of La4Ni3-xMnxO10 was prepared by solid state reaction. The crystal structure of La4Ni3-xMnxO10 was analyzed by powder X-ray diffraction and Rietveld methods. The solid solution for x=0.5 had a orthorhombic system with lattice parameter a=0.5485(0), b=0.5433(6) and c=2.8034(9). In detailed observation of the X-ray diffraction data, some superlattice reflections that were forbidden for a face centered orthorhombic cell were identified. A possible space group Pnnn (no.48) was derived from the reflection conditions.