In previous work the authors have shown that A13 β-Mn precipitates having a simple cubic structure were formed in an Fe-9. 1A1-29.9Mn-2.9Cr alloy after being solution heat treated and aged at 525°C or above. A13 β-Mn precipitates prefer to nucleate in a heterogeneous manner, predominantly on small-angle ferrite/ferrite grain boundaries, dislocations and at the regions contiguous to the DO3 particles. As aging time increased, the precipitates grew rapidly along certain preferred orientations. The purpose of the present investigation was to study the orientation relationship between A13 β-Mn precipitate and the ferrite matrix. The long-axes of A13 β-Mn precipitates within the ferrite matrix were also determined.