Cassava starch waste from factories. It was found that the residue after fermentation art with the bacteria Clostridium clan and the product is butanol Which can produce as fuel.Butanol that has the ability to absorb moisture. Evaporation is low and also the density of energy similar to gasoline This project has a concept to study using cassava residue was fermented with Cl infections.Acetobutylicum by studying the concentration of bacteria Cl. Acetobutylicum found that bacteria Cl. Acetobutylicum concentration 106 has the ability to produce organic solvents as much as possible. However, the yield (Yield) of bacteria Cl.Acetobutylicum used different concentrations, which found that the yield (Yield) will increase from 0.19% 0.31% when the concentration of bacteria. Cl. Acetobutylicum from 104 CFU / ml is 105 CFU / ml and will increase from 0.31% 0.35% increase in the concentration of bacteria Cl. Acetobutylicum from 105 CFU / ml is 106 CFU / ml and decreased from 0.35% 0.32% when increase the concentration of bacteria. Cl. Acetobutylicum from 106 CFU / ml is 107 CFU / ml from data using the concentration of bacteria Cl.Acetobutylicum. In the production of organic solvents at high concentration. It will affect the amount of butanol. So when we increase the concentration of bacteria Cl. Acetobutylicum too high will result in the production of decrease.