Abstract: Abstract: Scanning electron microscopy (SEM) and terahertz time domain spectroscopy (THz-TDS) were employed to investigate the effects of steam-explosion on biomass, and the surface images, micro-analysis and terahertz spectra were obtained. SEM analysis of the surface showed that the parenchyma cell and epidermis of corn stem were smashed and separated by steam-explosion, which suggests a great increase in specific surface area and potentially enhanced speed of fermentation in the production of biogases and biofuels. Terahertz spectra of stover showed that their absorption coefficients increase with increasing frequency. Steam explosion may cause a subtle chemical change in biomass according to obviously different absorption coefficients between the steamed and original samples, which could also be proved by micro-analysis. Moreover, two resonance peaks were detected in the absorption curves of parenchyma cell, with notable frequency shift between curves of the steamed and original parenchyma cells. Assignments of the two vibrational peaks must be explored by further studies.