An automatic transmission oil composition includes 80 to 85 wt % of a base oil, 1 to 5 wt % of metallocene polyalphaolefin, 1 to 5 wt % of a detergent-dispersant, 0.01 to 0.03 wt % of a trinuclear molybdenum-based dialkyldithiocarbamate friction modifier, 3 to 10 wt % of a viscosity modifier, and 3 to 5 wt % of an anti-wear additive. The automatic transmission oil composition is prepared by mixing base oil with metallocene polyalphaolefin and a trinuclear molybdenum-based dialkyldithiocarbamate friction modifier at specific mixing ratios, whereby the dynamic friction coefficient can be maintained at an equivalent level and the metal friction coefficient can be reduced, thus improving the power transfer efficiency between transmission metals and fuel economy (an improvement of 1.5% or more), increasing durability, and minimizing energy loss.