The size-selective Zr2Sin (n = 16-24) caged clusters have been investigated by density functional approach in detail. Their geometries, relative stabilities, electronic properties and ionization potentials have been discussed. The dominant structures of bimetallic Zr-2 doped silicon caged clusters gradually transform to Zr2 totally encapsulated structures with increase of the clustered, size from 16 to 24, which is good agreement with the recent experimental result (J. Phys. Chem. A. 2007, 111, 42). Two novel isomers, i.e., naphthalene-like and dodecahedral Zr2Si20 clusters, are found as low-lying conformers. Furthermore, the novel quasi-ID naphthalene-like ZrnSim nanotubes are first reported. The second-order energy differences reveal that magic numbers of the different sized neutral Zr2Sin clusters appear at n = 18, 20 and 22, which are attributed to the fullerene-like, dodecahedral and polyhedral structures, respectively. The HOMO-LUMO gaps (> 1 eV) of all the size-selective Zr2Sin clusters suggest that encapsulation of the bimetallic zirconium atoms is favorable for increasing the stabilities of silicon cages.