Antiferromagnetic spintronics actively introduces new principles of magnetic memory, in which the most fundamental spin‐dependent phenomena, i.e., anisotropic magnetoresistance effects, are governed by an antiferromagnet instead of a ferromagnet. A general scenario of the antiferromagnetic anisotropic magnetoresistance effects mainly stems from the magnetocrystalline anisotropy related to spin–orbit coupling. Here magnetic field driven contour rotation of the fourfold anisotropic magnetoresistance in bare antiferromagnetic Sr2IrO4/SrTiO3 (001) thin films hosting a strong spin–orbit coupling induced Jeff = 1/2 Mott state is demonstrated. Concurrently, an intriguing minimal in the magnetoresistance emerges. Through first principles calculations, the bandgap engineering due to rotation of the Ir isospins is revealed to be responsible for these emergent phenomena, different from the traditional scenario where relatively more conductive state is obtained usually when magnetic field is applied along the magnetic easy axis. These findings demonstrate a new efficient route, i.e., via the novel Jeff = 1/2 state, to realize controllable anisotropic magnetoresistance in antiferromagnetic materials. Controllable anisotropic magnetoresistance and concurrent magnetoresistance minimal are evidenced in Sr2IrO4 thin film, which is antiferromagnetic with strong spin–orbit coupling. First‐principles calculations reveal that bandgap engineering due to rotation of the Ir's isospins in the films is responsible for these two emergent phenomena.