Abstract: The results of experiments on the influence of a weak magnetic field on the sensitivity of powdered pentaammine (5-nytrotetrazolato-N₂) cobalt(III) perchlorate to a high-current electron beam of nanosecond duration have been presented. In the experiments, two types of pentaammine (5-nytrotetrazolato-N₂) cobalt(III) perchlorate powder were used: medium- and fine-dispersed ones. It has been found that both the weak magnetic field and the powder dispersion affect the sensitivity to the high-current electron beam.