The bio-electrode for L-asparagine, excellent in the reproducibility of responsibility, has been constructed by immobilizing the bacterium Proteus mirabilis on an ammonia gas sensor. This electrode was investigated for the effects of pH, temperature, buffer solution, bacterial amounts and interferences, and stability with the lapse of time. The response of the bacterial electrode was linear in the range of $9.0{ imes}10^{-5}$ ∼ $1.0{ imes}10^{-2}M$ L-asparagine with a slope of 58.9mV/decade in pH 7.8, 0.05M phosphate buffer solution at $30^{circ}C$. The bacterial amounts used for this electrode was 3 mg and response time was 7∼9 min. Therefore, this assembly can be used for the determination of L-asparagine.