An analytical method for trimethylamine in ambient air was developed, using headspace gas chromatography with flame ionization detection. Trimethylamine was collected on the acid filter which was impregnated sulfuric aicd in the 47 ㎜ diameter of glass fiber filter. Trimethylamine collected on the acid filter was regenerated in the headspace vial and introduced into the GC analytical column directly. Several parameters such as sample volume, equilibrium temperature and time, and slurry method of filter were optimized to provide maximum detection response. Resolution power also compared according to liquid phase of analytical column. The detection limit of method was 0.13 ppb with 50 L sampling volume. The developed acid filter method is easy to deal with the field sampling and the method was adopted as the standard method for odor analysis in Korea.