Organic ionic plastic crystals (OIPCs) have been studied as solid-state electrolytes owing to their desirable properties such as plasticity, non-flammability, and high ionic conductivity. However, the relationship between the ion structures and the properties of OIPCs are poorly understood. To supplement our previous work on the effects of the side chain structure of pyrrolidinium salts on their properties, this study examined the effects of the anion structure. For this purpose, five N,N-diethylpyrrolidinium ([C(2)epyr]) salts with various sulfonylamide anions were synthesized. The [C(2)epyr] salts with bis(fluorosulfonyl)amide ([FSA]) and bis(pentafluoroethanesulfonyl)amide ([BETA]) exhibited higher ionic conductivity values at room temperature than the other [C(2)epyr] salts. The H-1 and F-19 solid-state NMR results indicated that the component ions in [C(2)epyr][FSA] and [C(2)epyr][BETA] exhibited high rotational mobility, even in the solid state. Thus, rotational mobility is likely important for achieving high ionic conductivity.