In this paper, alkaline hydrothermal conversion of glucose, a model compound of carbohydrate biomass, into lactic acid was discussed. Results showed that both NaOH and Ca(OH)(2), can promote the formation of lactic acid in a hydrothermal reaction of glucose. In the case of the addition of NaOH, lactic acid was obtained with a yield of 27% based on a starting carbon mass of glucose at 300 degrees C for 60 s with a NaOH concentration of 2.5 M. In the case of the addition of Ca(OH)(2,) the highest yield of lactic acid is 20%, which occurred at 300 degrees C for 60 s with a Ca(OH)(2) concentration of 0.32 M. The formation mechanisms of lactic acid from glucose were also discussed according to intermediate products identified, to examine if lactic acid is also formed via the aldose having one and two carbon atoms besides via the aldose having three carbon atoms. Result showed that lactic acid may be generated via formaldehyde, glycolaldehyde besides via the aldose having three carbon atoms in hydrothermal reaction which all formed by the reverse aldol condensation of hexoses.