Chromium poisoning is one of the critical issues leading to the degradation of LSCF. In this work, the poisoning experiment is carried out for 100 h with a low concentration of Cr source at a temperature of 700 °C. We focus on the detection of the secondary phases after poisoning using high-resolution electron microscopy techniques. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) results indicate that there seem to be Cr/Sr-rich particles formation on the surfaces of grains. Scanning transmission electron microscopy-EDS analysis confirms that such particles are SrCrO4. They form on the cathode surface and the entire cathode layer and are found mainly at the grain boundaries of LSCF open to the gas phase. The related instability of LSCF before and after poisoning is also discussed.