The stable isomers of Mon (n=2∼15) are determined by using genetic algorithm combined with DFT calculations. Some new ground-state structures are found. The 3D structure firstly appears for Mo4 and the distorted pyramid or prism isomers are energy favored for n = 4∼9, while icosahedron-like or cage-like structures are dominant for n = 10∼15. Mo3, Mo5, Mo7, Mo8, Mo11 and Mo13 are magic number clusters. There are small magnetic moments and vertical electron affinity but large vertical ionization potential for Mon. The electronic structure analysis indicates that there form strong Mo-Mo covalent bonds, which are also delocalization to a certain extent due to the 4d and 5s orbital hybridization. The IR and UV–vis spectra are acquired and the particularly large hyper polarizability of Mo9 also suggests that it can be used as a nonlinear optical material.