Abstract: A simplified apparatus for the determination of specific surface area by nitrogen adsorption has been constructed, The correction factor for non-ideality of nitrogen gas used is calculated by a formula derived by the author.This apparatus is simple and convenient for routine work, the calculation can be simplified by using tables and a curve, On the basis of a large number of data, the percentage standard error has been calculated to be 2.2~6.7%, lower than 2.8~14.5% in the British standard for similar apparatus.