A new laser based inspection system (LIVVS) has been developed by ENEA for periodic in-vessel inspection in large fusion machines. The design has been taking into account the radiation levels, operating temperatures and pressures forseen in large European fusion machines such as JET (Joint European Torus) and ITER (International Thermo-nuclear Experimental Reactor). Tests on the LIVVS mock-up are in progress in order to assess the mechanical, optical and electronic performances, and so to measure the system accuracy. Following a detailed mechanical description, preliminary results are reviewed and discussed.