Abstract: A test method for the determination of methanol content in B-100 biodiesel by headspace gas chromatography has been established. The B-100 biodiesel sample was dissolved in N,N-dimethylacetamide and equalized at 90 ℃ for 45 min in the head-space sampler,then separated and determined on a gas-chromatograph through a HP-INNOWax capillary column. An external standard quantitative formula was established with the correlation coefficient more than 0.999. The limit of quantitation is 0. 005%. The relative standard deviations(n = 6) were between 4.96% and 6.83%. The recoveries was between 92% and 110%. This method is simple,rapid, accurate, and can be applied to the determination of methanol content in B-100 biodiesel.