We have been investigating about life cycle assessment (LCA) of pulp and paper products. In this investigation, we have been using to the calculation of life cycle inventory (LCI) data for LCA from our mill operation data, our laboratory research data and the reference data. In this paper, we introduced firstly, some LCI data from reference literatures, and secondary, about our calculation method of accumulation from practical mill operation data, laboratory research data and some reference data. Finally, we compared with LCI data about pulp and paper products of literatures and our calculation results. In this comparison, we found there were nearly equal results by our calculation method of accumulation and other methods.