Chemical composition of two ecotypes of the Vetiver grass (Vetiveria zizanioides nash) leaves has been investigated using the gravimetric method. The principal polysaccharides found in samples were hemicelluloses (ca. 38%), followed by cellulose (ca. 27%). Protein content determined by bicinchoninic acid assay using bovine serum albumin (BSA) as a standard was approximately 5%. Lignin content determined by acid chlorite method was approximately 10%. Ash content was 3% consisting of mainly silica (ca. 50%). The obtained hemicelluloses with the molecular weight of 30,000 showed the decomposition temperature at 310 °C. In order to determine an optimum condition for extraction of hemicelluloses, effects of process parameters: alkaline type (NaOH, KOH, Ca(OH)2 and Ba(OH)2), alkaline concentration (0.025–4 M), extraction time (2–18 h) and temperature (25–60 °C) were studied. It was found that all parameters influenced on the hemicellulose yield and properties in various degrees. Finally, an optimum condition giving a maximum yield of 35% hemicelluloses was recommended as 4 M NaOH at ambient temperature for 8 h.