Low optical loss (<dB/cm) thin films of Corning 7059 glass have been prepared by electron beam deposition and by rf magnetron sputtering. The effects of gas pressure, deposition power and oxygen-to-argon ratio on refractive index and optical loss were studied. Deposition rates obtained with the sputtering process were about 0.2 nm/sec while much higher deposition rates (2 nm/sec) were obtained with electron beam deposition. The films were found to be amorphous in structure. The refractive index of electron beam-deposited films was measured as 1.50 while the sputtered film index was measured as 1.525. Film composition and composition profiles determined by RBS, electron microprobe and neutron activation analysis are presented. Sputtered films show uniform elemental composition profiles for Si, Ba, B and Al. Electron beam-deposited films have uniform composition profiles if the deposition power is kept constant. The rms surface roughness of the films, measured using an optical profilometer, is 1 nm. The contributions of surface roughness and cladding layer thickness to optical loss are discussed. The major source of optical loss in sputtered films is light absorption.