This research was to study the color removal efficiency of a 12 1anaerobic-aerobic SBR process treating an azo-reactive dye. The ratio of influent(V(,f)) to remaining volume (V(,o)) was 2: 1. The anaerobic, aerobic and settlingtimes were set at 18, 5 and 1 hr, respectively. The EBPR promoting and non-promotingsubstrates were used, i.e., nutrient broth + sodium acetate (in term of COD) at500+0, 350+150, 250+250 and 0+500, as PAOs promoting substrate, and glucose (500 mg/lCOD, Experiment G1), as GAOs promoting substrate. The nitrogen and phosphorus ininfluent were 50 mg-N/l and 15 mg-P/I, respectively. Besides, nitrogen and phosphorsin influent were also varied to be 25 mg-N/l and 5 mg-p/l (Experiment G2) (COD:N:P =100:5:1) in order to inhibit EBPR and promote GAOs in the system. The anaerobic,aerobic and settling times were also varied to be 6, 5 and 1 hr (Experiment G3) inorder to observe the effect of the anaerobic time. Remazol Black B dye at 10 mg/lconcentration was used in all experiments. The sludge age of the system wascontrolled at 8 days. At steady state, the efficiency of color removal for the cases of nutrientbroth + sodium acetate at 500+0, 350+150 250+250 and 0+500 and experiment G1, G2 andG3 was 73.3, 71.7, 71.4, 70.6, 67.8, 66.3 and 63.1 % in terms of SU and 76.7, 73.4,73.0, 69.0, 66.2, 64.4 and 59.0 % in term of ADMI, respectively. It showed thatdifferent substrates and anaerobic time had effects on the degree of color removal.The experiment using nutrient broth + sodium acetate as substrates was better indecolorisation than those with glucose. Long anaerobic time (18 vs 6 hr) was betterfor the color reduction. But the color removal efficiencies of PAOs and GAOs were notdifferent. The high COD removal efficiency was in the range of 91.7 - 97.3 % for allexperiments. The efficiency of TKN removal was 97.6, 96.3, 96.6, 42.6, 92.6, 90.7 and95.6 %, respectively. In the experiment 0+500, the organic carbon removal efficiencyin anaerobic stage was not as good as other cases. So high residual organic carbonwas presence in the beginning of the aerobic stage and nitrification could not occur.The efficiency of phosphorus removal was 99.3, 100, 78.7, 45.9, 67.7, 98.1 and 38.7%, respectively, which was in line with the theory of substrates, concentrationsubstrates and nutrients and anaerobic time.