In this paper, a novel design approach for significant size reduction of a class of dual-band branch-line coupler (BLC) by use of a transmission line model loaded with a folded-T-type stepped-impedance-stub (FTTSIS) is proposed. At the first step, by loading FTTSIS at the middle of each branch instead of stepped-impedance-stub (SIS) in the conventional branch-line coupler, a compact dual-band BLC with same performance that is about 65% of the conventional one is achieved. Then by mirroring the FTTSISs of 35Ω lines inside the inner space of the proposed structure, miniaturized dual-band BLC that is only 30% of the conventional dual-band BLC operating at same WLAN frequencies is obtained. The proposed structure is then fabricated and measured. The measurement results show good agreement with the theoretical ones.