L(+) lactic acid have been used in pharmaceutical, textile, tanning, food industry and in the biodegradable plastics synthesis. A Plackett-Burman design was applied to screen seven parameters, corn steep liquor, sodium acetate, magnesium sulphate, manganese sulphate, ammonium citrate, potassium phosphate and tween 80, for significant factors for the production of L(+) lactic acid by Lactobacillus rhamnosus using cassava flour wastewater. These experiments were carried out in 250 mL Erlenmeyers flasks containing 45 mL of fermentation medium at 37°C, 200 rpm, an initial pH of 6.5. After 48 hours, samples of 1 mL were withdrawn from fermentation broth. The biomass concentrations were determined by dry weight. Lactic acid and total sugar concentrations were determined by a high performance liquid chromatography system equipped with UV detector at 210 nm and IR detector. A Rezex ROA (300 x 7.8 mm, phenomenex) column was eluted with 5mM H₂SO₄ as a mobile phase with a flow rate of 0.4 ml/min and the column temperature was maintained at 60 °C. The variables, corn steep liquor and Tween 80, had a significant influence on production, which were further optimized for increased L(+) lactic acid production, using response surface methodologies involving central composite designs. The best L(+) lactic acid production (41.61 g/L) were obtained with 68.2 g/L of corn steep liquor and 0.1% of tween 80.