The Vetier (Vetiveria zizanioides) cellulose micro/nano fibrils (VCMNFs) were isolated by high intensity ultrasonication (HIUS). The morphology and diameter distribution of cellulose fiber and micro/nano fibrils were investigated by optical microscopy, scanning electric microscopy (SEM) and laser diameter analysis instrument. The range of diameter distribution of micro/nano fibrils was from 0.24 μm to 426 μm. With the variation of treating amplitude and time by HIUS, the extent of fibrillation and diameter distribution were different. There were significant changes of diameter distribution treated at amplitude of 90% and 30 min or 60 min and the diameter distribution was showed from 7.0 to 80 μm.