Thermal stability of Fe-P-C-B-Al-Ga glassy alloys with effect of additional elements(Al, Ga) were investigated. The dissolution of 5 at% Al and 2 at% Ga for the Fe_(79-x-y)P_(11)C_6B₄Al_xGa_y alloy was found to be effective for the extension of the supercooled liquid region defined by the difference in the glass transition temperature(T_g) and crystallization temperature (T_x), ΔT_x(=T_x-T_g). The ΔT_x value is 30 K for the Fe-P-C-B alloy and is increased to 61 K for 5% Al and 2% Ga. The effectiveness of addition Al and Ga is presumably due to the combination effects of ; (1) the difficulty of atomic rearrangements for the precipitation of the Fe-metalloid compounds caused by the generation of Al-metalloid pairs with strongly attractive bonding nature, and (2) the decrease in the preferential precipitation tendency of Fe-B, Fe-C compounds by the dissolution of Ga which is immiscible to B and C and soluble to Fe.