Provided is a precision press-molding optical glass that is not easily degraded in quality by the occurrence of an altered layer such as fogging or yellowing on a surface and that comprises B.sub.2O.sub.3, ZnO, La.sub.2O.sub.3 and ZrO.sub.2 and contains, by mol %, 0 to less than 0.5% of Li.sub.2O, 20 to 50% of B.sub.2O.sub.3, 0 to 20% of SiO.sub.2, 22 to 42% of ZnO, 5 to 24% of La.sub.2O.sub.3, 0 to 20% of Gd.sub.2O.sub.3, provided that the total content of La.sub.2O.sub.3 and Gd.sub.2O.sub.3 is 10 to 24%, 0.5 to 10% of ZrO.sub.2, 0 to 15% of Ta.sub.2O.sub.5, 0 to 20% of WO.sub.3, 0 to 15% of Nb.sub.2O.sub.5, 0 to 20% of TiO.sub.2, 0 to 10% of Bi.sub.2O.sub.3, 0 to 10% of GeO.sub.2, 0 to 10% of Ga.sub.2O.sub.3, 0 to 10% of Al.sub.2O.sub.3, 0 to 10% of BaO, 0 to 10% of Y.sub.2O.sub.3 and 0 to 10% of Yb.sub.2O.sub.3, the optical glass having an Abbe's number (.nu.d) of at least 35 but less than 40.