Cellulosic biofuels can be used as transportation fuels. But their manufacturing cost is high, partly because the low density of cellulosic feedstocks causes their transportation and handling costly. Ultrasonic Vibration-Assisted (UV-A) pelleting can increase the density of cellulosic feedstocks. However, charring of biomass sometimes happens during UV-A pelleting and may adversely affect the yield of biofuel conversion. This paper reports an experimental investigation on charring of cellulosic biomass in UV-A pelleting. It studies effects of moisture content of the biomass and pelleting variables. The results will be helpful when selecting pelleting conditions to avoid biomass charring.