Ta2O5 films were deposited onto unheated glass substrates by reactive low voltage ion plating (RLVIP). From the amorphous films with thicknesses between 200 and 300 nm the optical properties (refractive index n, absorption coefficient k) and the mechanical properties (relative density rho and intrinsic stress sigma) were investigated in dependence on the relation between working gas pressure (Ar) and the reactive gas pressure (O-2). The films had k-values lower then 4 x 10(-4) at 550 nm at a gas pressure composition of 0.8 x 10(-3) mbar Ar and 2.0 x 10(-3) mbar O-2. With low total pressure high refractive indices, high compressive film stress and a high relative film density were found all decreasing with increasing gas pressure. A post deposition heat treatment at 350 degrees C on air during 4 h resulted in a remarkable decrease in the refractive index and the film stress.