Antiperovskite bulk materials show attractive properties and have potential applications on the magnetic sensor, zero thermal expansion, and magnetocaloric effect. Hence, it is important to intensively study the materials on multiple dimensionalities. Herein, the Mn3SnC thick films with variable planar size are used for longitudinal resistivity, magnetization, and ferromagnetic resonance (FMR) properties study. An abnormal thermal hysteresis loop feature and angular‐dependant longitudinal resistivity of the Mn3SnC around the first‐order phase transition under in‐plane (IP) magnetic field for the first time are found. This abnormal thermal hysteresis loop is affected by magnetic field direction, IP angle, and field strength. The angular‐dependent longitudinal resistivity measurement implies that the electrical transport properties of Mn3SnC correlate with the IP magnetic field orientation and show high angular sensitivity. This novel feature of Mn3SnC relates to the spin‐Hall magnetoresistance. The discrepancy between IP and out‐of‐plane magnetization indicates the variable planer arrangement of Mn atoms, which affects magnetic interactions. The dynamic property of FMR is studied on the Mn3SnC sample, and the phase transition temperature is consistent with that of the electrical transport and magnetization study.