Kariba weed (Salvinia molesta) was used as biomass for ethanol production by separate hydrolysis and fermentation (SHF). Monosaccharides from Kariba weed hydrolysate was produced using thermal acid hydrolysis, sonication and enzymatic saccharification. The optimal conditions for thermal acid hydrolysis of 12% (w/v) Kariba weed slurry were evaluated as 200 mM HNO₃ at 121℃ for 60 min yielding 10.2 g/L monosaccharides. Sonication for 45 min before enzymatic saccharification, yielded more monosaccharides of 18.7 g/L. Enzymatic saccharification with 16 U/mL Cellic CTec2 produced 35.4 g/L monosaccharides. Fermentation was performed with Saccharomyces cerevisiae, Kluyveromyces marxianus or Pichia stipitis with sonicated Kariba weed hydrolysate. The control fermentations were carried out using Kariba weed hydrolysate without sonication. The improvement of ethanol production from sonicated Kariba weed hydrolysate using P. stipitis produced 15.9 g/L ethanol with ethanol yield coefficient, YEtOH = 0.45, K. marxianus produced 14.7 g/L ethanol with YEtOH = 0.41. S. cerevisiae produced the lowest yield of 13.2 g/L ethanol with YEtOH = 0.37 as it utilized only glucose not xylose. Sonication of Kariba weed is essential in the ethanol production to enhance the productivity of monosaccharides. P. stipitis is the best yeast using hydrolysates with the mixture of glucose and xylose to produce ethanol.