O ne of many ways to decreasing ammonia in wastewater is by using biologically process, which is by nitrification and denitrification. Both process only works in present of microorganism, for example nitrosomonas and nitrobacter.The wastewater that contains ammonia if not be treated will cause pollutions in water body where those waste dumped. Nitrogen in form of organicN will be transform to ammonium in water. On the next process those ammoniumwill be transform again biologically to nitrite (N02) and nitrate (N03)by microorganism activity, where all the process called Nitrification.The aim of this researcn is to know which is the right composition from concentration of microorganism culture and concentration of molasses in ammonia CNH3) decreasing process. Tile variations of microorganism culture in this research are 0.5 L, I L, 1.5 L, 2 L and tile variations of molasses concentration are 5 %, I 0 %, 15 %, 20 %.;...... _The seeding and acclimatization process in this research is stopped when the microorganism concentration has achieved 6401 mg :MLVSS/L and 4277 mg MLVSS/L. on every variable of molasses is variated with each variable microorganism culture, except in 20 % and 5 % concentration. Because it has been known that 1 L microorganism culture is the best variable. Every research is done in the same condition which is reactor operated in volume of 46 L and the flow is 2.16 m3/day and runs under the .same neutral condition (pH= 7). With composition of I L microorganism culture and I 0 % of molasses concentration, the result shows that 66.84 % efficiency of nitrogen removal. To look at the nitrogen concentration in the effluents which is still not qualified under the government standard, the next treatment is needed by modifications on the reactor or by adding others treatment unit to gain better results.