Excessive amounts of fast-growing water hyacinth have densely invaded many canals, lakes, and rivers throughout Thailand, damaging the ecology of local waterways. Water hyacinth is a typical lignocellulosic material and is recognized as a potential source of renewable energy. In this study, hydrothermal pretreatment accompanied by enzymatic hydrolysis of dried water hyacinth is investigated in the temperature range 160-220 degrees C, using a hydrothermal ball-mill reactor; this enables hydrothermal pretreatment and ball-mill pulverization to be conducted simultaneously. The effects of CH3COOH and K2CO3 on the liquid composition were investigated experimentally (CCH3COOH = 0.5-1.0 wt %, C-K2CO3 = 0.5 wt %). In the absence of CH3COOH and K2CO3 at 220 degrees C, a glucose yield of 0.267 was obtained. The highest glucose yield of 0.855 was achieved at 200 degrees C with C-CH3COOH = 0.75 wt % and water hyacinth intake = 10 wt %. In the presence of 0.5 wt % K2CO3, a glucose yield of 0.195 was obtained at 220 degrees C. The addition of K2CO3 did not suppress hydrolysis in the hydrothermal pretreatment. The autocatalytic effect of acid production in the hydrothermal pretreatment is therefore not large. A pseudofirst-order kinetic model with regard to cellulose content was developed to explain the conversion mechanism of cellulose to glucose in the hydrothermal pretreatment process.