Disclosed are an optical fiber unit in which at least 1-core optical fiber is mounted in and protected by a buffer tube, and an optical cable including the optical fiber unit. The buffer tube is made of a mixture, which includes a composite resin including a resin selected from polyolefin polymer, nitrile rubber and their mixture, and plasticized polyvinylchloride; and an inorganic additive, wherein, in a stress-strain curve of the buffer tube, a modulus is 5 to 50 kgf/mm² in a linear region with an elongation less than 1% and a tan is less than 0.5 at 30 C. The buffer tube of the optical fiber unit may be very usefully applied to an optical cable because it may be easily cut out to ensure easy contact and gives excellent elasticity without being crushed by lateral pressure.