With　the　rapid　development　of　narrow　band　power　line　communications　(NPLC)　in　recent　years,　many　effective　modulation　schemes　have　been　proposed　for　it.　In　this　paper,　we　propose　M-ary　differential　chaotic　shift　keying　(M-DCSK)　for　Narrow　Band　(NB)　PLC.　Firstly,　which　improves　the　bandwidth　efficiency　compared　with　DCSK　scheme.　The　performance　of　M-DCSK　scheme　is　analyzed　over　PLC　channels　where　background,　impulsive　and　phase　noise　exist.　Simulation　results　verifiy　the　accuracy　of　the　derived　theoretic　performance.　Due　to　the　inner　properties　of　chaotic　carrier,　M-DCSK　shows　good　robustness　against　multipath　fadings　and　phase　noises,　which　are　very　common　in　PLC　channels.　Besides,　comparing　with　the　traditional　direct　sequence　M-ary　differential　phase　shift　keying　(DS-MDPSK)　scheme,　M-DCSK　can　achieve　better　bit　error　rate　(BER)　performances.