Cation-pi　interactions　have　proved　to　be　important　in　proteins　and　protein-ligand　complexes.　Here,　cation-pi　interactions　are　analyzed　for　282　non-redundant　protein-RNA　interfaces.　The　statistical　results　show　that　this　kind　of　interactions　exists　in　65%　of　the　interfaces.　The　four　RNA　bases　are　ranked　as　Gua　＞　Ade　＞　Ura　＞　Cyt　according　to　their　propensity　to　participate　in　cation-pi　interactions.　The　corresponding　ranking　for　the　involved　amino　acid　residues　is:　Arg　＞　Lys　＞　Asn　＞　Gln.　The　same　trends　are　obtained　based　on　the　empirical　energy　calculation.　The　Arg-Gua　pairs　have　the　greatest　stability　and　are　also　most　frequently　observed.　The　number　of　cation-pi　pairs　involving　unpaired　bases　is　2.5　times　as　many　as　those　involving　paired　bases.　Hence,　cation-pi　interactions　show　sequence　and　structural　specificities.　For　the　bicyclic　bases,　Gua　and　Ade,　their　5-atom　rings　participate　in　cation-pi　interactions　somewhat　more　than　the　6-atom　rings,　with　percentages　of　54　and　46%,　respectively,　which　is　due　to　the　higher　cation-pi　participation　proportion　(63%)　of　5-atom　rings　in　the　paired　bases.　These　results　give　a　general　view　of　cation-pi　interactions　at　protein-RNA　interfaces　and　are　helpful　in　understanding　the　specific　recognition　between　protein　and　RNA.