The sterilization of a small vial using electron cyclotron resonance (ECR) plasma was investigated. The ECR plasma was generated throughout the inside of the small vial, which was sealed with nonwoven fabric, by using magnetic configuration in which the ECR point was located inside the small vial. Moreover, it was demonstrated that the temperature of the small vial was finely controlled by the pulse width and pulse frequency of the pulsed microwave power. A biological indicator (BI), Geobacillus Stearothermophilus, containing 1 x 10(5) spores present inside the small vial was successfully inactivated in a total treatment time of about 14 min while maintaining treatment temperature of less than 65 degrees C.