The possibility of using abundant metal chlorides as a single reagent for pretreatment and degradation of switchgrass biomass was studied. Three metal chlorides: MgCl2, CaCl2 and FeCl3 were tested in the initial phase and FeCl3 at 2% w/w loading was found as the most effective reagent for treatment and hydrolysis of switchgrass in hot compressed water. Therefore, FeCl3 was selected for the detailed study and the heat treatment at 140–160 °C or microwaving for 6–10 min was required to activate the FeCl3 after impregnation of switchgrass. These samples could be hydrolyzed in water at 160 °C, without additional catalyst or reagent to produce reducing sugars. In the hydrolysis experiments, FeCl3 impregnated and micro waved switchgrass produced slightly higher total reducing sugar (TRS) yields of 31.5%; whereas the samples heated at 140 °C after FeCl3 impregnation produced 28.6% TRS yield. In a thermogravimetric analysis study, the decomposition temperature of lignin fraction showed the highest shift (ΔTdecomp ~ - 42 °C) after adding 2% w/w FeCl3 and microwaving for 10 min, indicating that strong interactions between FeCl3 and lignin is likely the primary cause of enhancement in polysaccharide degradation.