The present invention relates to an olefin-based polymer, wherein (1) the density (d) is 0.850-0.865 g/cc; (2) the melt index (MI) (190°C and 2.16 kg load conditions) is 0.1-3.0 g/10 min; and (3) the hardness, density, and melt temperature (Tm) satisfy mathematical formula 1 and mathematical formula 2 or 3. The olefin-based polymer according to the present invention, which is a low-density olefin-based polymer, has low hardness and thus exhibits improved foam characteristics and impact strength at the time of compounding.