The phase diagram in the system La-Se was investigated around the LaSe 2 composition. X-ray and microprobe analyses reveal the existence of only two phases, LaSe 2 and LaSe 1 . 9 , with no solid solution behavior between them. Infrared and Raman spectra of the non-stoichiometric phase suggest that the vacancies in the basal plane of the low-dimensional lattice are disordered. Polarized single crystal Raman spectra and a modified valence force field calculation for LaSe 2 indicate that the assumption of isolated (Se-Se) 2 - pairs in the anti-Fe 2 As structure is not justified. In accord with this, the observed resistivity for LaSe 2 as a function of temperature is typical of a semimetallic compound. A transition to a semiconductor may occur below 110 K. The measured resistivity as a function of temperature for the non-stoichiometric LaSe 1 . 9 phase is indicative of a semiconductor. The infrared data together with the electrical measurements suggest that this phase can be considered as n-type semiconductor with the holes in the anionic sp valence bands.