To provide an optical film having appropriate optical characteristics and a high polarizing plate protection effect, a method for producing the same, a durable polarizing plate using the same and a liquid crystal display device.

The optical film contains a cyclic olefin resin and 5 mass% of an additive based on the cyclic olefin resin and has a product of a water content and an oxygen transmission rate of 6,000, wherein the water content is an equilibrium water content after preservation at 25C and 60% RH for 24 h, and the oxygen transmission rate is an oxygen transmission rate measured by a MOCON method.