Abstract: The shelflife of 25% ascorbic acid injection was predicted by accelerated stability test with the classical isothermal method (at 98, 90, 80 and 70℃). The experimental data were treated with four methods to estimate the shelflife, i. e, calculation from equation of exponential function, equation of second power function and Weibull distribution function; and direct derivation from the inverse sigmoid curve. These methods were based on the rate equation of coloration. The predicted shelflives obtained by the above four methods coincided well. The shelflife was about 30 months, and also coincided with the value obtained from samples reserved for observation at room temperature.