<p>The effect of magnetic field aging on the microstructure of the polycrystalline Fe-Mn-Al-Ni-Ta-B alloy has been investigated with its impact on superelasticity. Specifically, its microstructure evolution including the appearance of beta-Mn phase, the significant increase in dislocation density, and the suppressed growth of nanosized ordered precipitates in an alloyed version of the Fe-Mn-Al-Ni alloy aged at 1 T, was elucidated by a comparative study with that alloy aged at 0 T. For the parallel-aligned beta-Mn phase, the premature at low aging temperature exerted fluctuations in components, induced a high density of dislocations in dual phases, leading to an enlarged martensitic transformation loop of thermal hysteresis. For the nanosized precipitates, a dramatic decrease in average size and their growth suppressed the increase in anti-phase boundary revealed their strong pinning effect, resulting in a reduction in the reversible motion of the austenite/martensite (A/M) interface. Evidence of the deteriorous reversible motion of A/M interface induced by magnetic field aging demonstrated the origin deduce in the superelasticity for that alloy. Regarding the detrimental effect in martensitic transformation and superelasticity, our findings detail the useful insights into the regulation and tailoring the service performance of FeMnAlNi-based superelastic alloys in the low magnetic field (e.g., geomagnetic field) regime.</p>