Abstract: AES with spark light source was applied to the determination of carbon in low contents in ferritic stainless steels. Through optimization of conditions of the method, the following points were emphasized: ① sampling was done by mold-casting, and the portion cut at the lower part of the mold 1/3 along its height was taken as sample which should be free from physical defects and enough for 2 excitation points on its surface without overlapping; ② the surface of the sample should be ground with miller using definite working parameters; ③ before analyzing the sample, a blank test with a low-carbon sample should be done to clear the counter electrode; ④ the carbon spectrum of 156.1 nm was chosen as the analytical spectral line to avoid the interference of aluminum; ⑤ the interference caused by high-contents of chromium was corrected by the correction formula given; ⑥ a set of standard samples covering carbon contents from (w) 0.003 2% to 0.038 3% was prepared for use specially in the preparation of the working curve. Four samples of ferritic stainless steels were analyzed by this method, giving results in consistency with those found by high frequency infrared absorption spectrometry and values of RSD′s (n=11) less than 8%.