A rapid and convenient methylation method of saccharin was developed to determine its content in foods by gas chromatography. Saccharin was methylated with trimethylsilyldiazomethane (TMSD) at room temperature for 10 min. N-Methylsaccharin formation rate from saccharin with TMSD was about 84%. N-Methylsaccharin was analyzed with FID-gaschromatograph by using a column of 3% SE-30 on Uniport B or 10% OV-351 on Uniport HPS. Anthracene was used as an internal standard for gas chromatography. The recoveries of sodium saccharin from soy-sauce spiked at 250 μg/g were 93.7±2.5% (n=5). Those from scallion pickles (rakkyo) spiked at 500 μg/g were 96.9±1.9% (n=5). The detection limit of saccharin in foods was about 20 μg/g as sodium saccharin. The analytical results obtained with this method agreed with those obtained by using diazomethane on methylation of saccharin (γ=0.998, n=10).