We investigate the low temperature anion exchange behavior of hydride and oxide in perovskite oxynitrides. CaH2 reduction of (Sr1–xLax)Ti(O3–xNx) (0<x ≤ 1) resulted in the selective anion exchange of hydride for oxide rather than nitride, yielding the oxyhydride-nitride (Sr1–xLax)Ti(O3–x–yHyNx). However, the exchange of hydride is drastically suppressed with increasing nitrogen content and is completely impeded when the nitride content reaches 10% of the anionic site. This implies that the N3– anions in the oxide lattice play a crucial role in lowering diffusion of O2–(and H–). The present study indicates the necessity to consider kinetic aspects when manipulating anion compositions, in particular in a mixed anion system with a small amount of anion vacancies.