The present invention discloses a stable retigabine which comprises (d) mixture of crystalline modification Form-A and modification Form-B or (e) mixture of crystalline modification Form-A and modification Form-C or (f) mixture of crystalline modification Form-B and modification Form-C, wherein the mixture of crystalline modification in (a) or (b) or (c) doesn"t convert to crystalline modification Form-A or modification Form-B or modification Form-C.