SUMMARYAlthough computer simulation is certainly a powerful tool for power system stability assessment, manual analysis is more helpful for understanding mechanism of unstable phenomena. Among unstable phenomena, oscillatory stability must be the most complex one. The paper analyzes the impact of recently developed Japanese RE's standard active anti‐islanding function named “frequency feedback with step injection” on power system oscillatory stability. Since active anti‐islanding makes islanded system unstable, it also makes stability of large interconnection worse. The question is how serious is the impact and how the impact can be mitigated. The paper presents a method for oscillatory stability analysis considering induction motor load, RE, and anti‐islanding function on RE so minutely as readers can reproduce. Analyses are performed as case studies on aggregated power sending and receiving systems in existing interconnection of Japan. The analyses results are verified by simulation results on the same case studies.