When recycling of disposed plastics products is investigated using LCA, the environmental assessment for recycling depends on how to specify its environmental load, In view of promoting the recycling of disposed plastics products such as PET bottles after use, it has been concluded to be reasonable that the cumulative CO2 emission unit defined as one of the environmental load indices for carbon dioxide should be specified as zero for disposed plastics products. Using the concept of cumulative CO2 emission units, the recycling of disposed PET bottles has been studied as a LCA problem and the following two conclusions have been confirmed. First, when the PET bottles are incinerated in open loop recycling, the latent energy of the petrochemicals is recovered while a large amount of CO2 is emitted to the atmosphere. Second, the use of recycled PET pellet contributes to decrease cumulative CO2 emission units in the production of carpet compared to the case where the virgin PET pellet is used.