A flow injection analytical system for monitoring the decomposition of beef was developed. The system included an immobilized enzyme reactor, in which tyramine oxidase was immobilized on controlled pore glass supports. Oxygen consumption involved in tyramine oxidase enzyme reaction was monitored. The carrier solution used was 0.1 M phosphate buffer (pH7.0). The detection limit was 0.02 mM, and the range for determination was 0.05-1.0 mM. The relative standard deviation was 1.8% for 10 successive determinations at 0.5 mM level. The determination frequency was 30 tests per hour. The immobilized enzyme also responded to tryptamine and phenethylamine, but did not show any reaction to dimethylamine, trimethylamine and hexamethylenediamine. When the system was applied to monitoring of the decomposition of beef, a steep increase of the response was observed between the storage period (2℃) of 12 days and 18 days. The system appeared to be useful for monitoring the decomposition of beef meat.