A 12-T magnetic field has been applied to a medium plain carbon steel during the diffusional decomposition of austenite and the effect of a high magnetic field on the distribution of misorientation angles, grain boundary characteristics and texture formation in the ferrite produced has been investigated. The results show that a high magnetic field can cause a considerable decrease in the frequency of low-angle misorientations and an increase in the occurrence of low R coincidence boundaries, in particular the R3 of ferrite. This may be attributed to the elevation in the transformation temperature caused by the magnetic field and, therefore, the reduction of the transformation stress. The wider temperature range for grain growth offers longer time to the less mobile R boundaries to enlarge their areas. Moreover, the magnetic field can enhance the transverse field-direction fiber (AE0 0 1aeiTFD). It can be assumed that the effects of the field were caused by the dipolar interaction between the magnetic moments of Fe atoms.