Largest percentages of ash were recorded in elephant grass before and after pretreatment. Experiments at 190 C for 10 min yielded the highest ash concentration (9.44%), whereas the lowest was obtained after pretreatment at 180 C for 10 min (2.77%). On the other hand, untreated elephant grass contained 8.53% of ash in its composition. Hence, it seems that lignocellulosic materials with an increased capacity to retain inorganic materials were generated under increased pretreatment severities and that these inorganic materials were not easy to remove even by extensive water washing.