Disclosed is uncrosslinked linear medium-density polyethylene resin composition for a power cable, which is applicable to an insulating layer, a semi-conducting layer or a sheath layer. Specifically, the uncrosslinked polyethylene composition includes: 100 parts by weight of a polymer comprising a linear medium-density polyethylene resin comprising an α-olefin having 4 or more carbon atoms as a comonomer and having a melt index of 0.6-2.2 g/10 min (at 190° C. under a load of 5 kg), a differential scanning calorimetry (DSC) enthalpy of 130-190 joule/g and a molecular weight distribution of 2-30; and 0.1 to 10 parts by weight of one or more additive(s) selected from a flame retardant, an oxidation stabilizer, a UV stabilizer, a heat stabilizer and a process aid.