Abstract: It is very difficult to analyze atmospheric nitrous oxied with common gas chromatograph (GC) because of its low concentration and the interference of O₂, H₂O and chloro-Fluoro-hydrocarbons. Therefore, a GC equipped with an electron capture detector (ECD) was modified for N₂O measurement. A 10-port valve for sampling and back flushing as well as a 4-port switching valve was incorporated into the GC System while a precoloum was used in combination with an analytical column. In addition, two absorbent traps were equipped in the inlet system to filter off H₂O and CO₂. In the proiect caried out in Beijing, China since November 1992 to monitor atmospheric nitrous oxide, the concentration of atmospheric N₂O in Beijing was analyaed with this modified system to be 317±12.8 ppbv.