To investigate the possibility of using biomass reductants instead of fossil fuels in the formation of direct reduced iron (DRI) in rotary hearth furnace (RHF), three kinds of cheap biomass such as bamboo char, straw fiber and charcoal were selected as reductants to compare with anthracite and graphite. The effect of reductants, temperature, dwelling time, C/O ratio and particle sizes on the shrinkage, strength and metallization of the biomass/ore pellets was investigated and discussed. The optimized reduction conditions were obtained as 1200 degrees C, 20min, C/O = 0.7 and the particle size range of <0.15 mm, 1-2 mm and 015-0.3 mm for straw fiber, bamboo char and charcoal respectively. The results showed that straw fiber was considered as an optimal reductant in the formation of direct reduced iron instead of fossil fuels. By the techniques of scanning electron microscope (SEM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD), the mechanism of biomass as reductants was revealed. Volatile matter was confirmed to play an important role in the formation of DRI when biomass used as reductants. (C) 2017 Elsevier Ltd. All rights reserved.