Provided is an
optical glass that has high-refractivity and high-dispersion properties and can give preforms for press-molding, which are excellent in shapability at high temperatures and suitable for precision press-molding.The optical contains, as essential components, 25 to 45 mol % of B2O3, 2 to 20 mol % of SiO2, 5 to 22 mol % of La2O3, 2 to 20 mol % of Gd2O3, 15 to 29 mol % of ZnO, 1 to 10 mol % of Li2O and 0.5 to 8 mol % of ZrO2, the
optical glass having a B2O3 / SiO2
molar ratio of from 2 to 5.5 and having an La2O3 and Gd2O3 total content of 12 to 24 mol % and a ZnO and Li2O total content of 25 to 30 mol %, the
optical glass having a
refractive index (nd) of 1.75 to 1.85 and an Abbe's number (νd) of 40 to 55, or the optical glass contains, as essential components, B2O3, SiO2, La2O3, Gd2O3, ZnO, Li2O and ZrO2 and has a
viscosity of at least 6 dPa·s at a
liquidus temperature thereof, a
glass transition temperature (Tg) of 600° C. or lower, a
refractive index (nd) of 1.75 to 1.85 and Abbe's number (νd) of 40 to 55.