Carbon fiber reinforced plastics (CFRP) have successfully been used in aerospace applications to replace heavier materials, because of their light weight, high strength and high rigidity. Although we strongly need the same benefits in automotive applications, the high price and the difficulty of the recycling process have inhibited its widespread use in the automotive industry, in particular mass-produced passenger cars. However, in the last few years, much work has been done in developing lower-cost CFRP. We thus used life cycle assessment (LCA) and calculated how much the environmental burden of conventional steel cars changed when we replaced steel with CFRP whose performance was proper for mass-produced passenger cars, and in addition when we recycled CFRP. Replacing steel with CFRP in bodies, chassis and equipment, we considered three cases: (1) Use of only CF/EP (Its matrix is epoxy, which is thermosetting.), (2) Use of CF/EP and CF/PP (Its matrix is polypropylene, which is thermoplastic.), (3) (2) and recycled CF/PP. For the assessment, a gasoline passenger car, with a total weight of 1380 kg, and with a useful lifetime of 91720 km, was chosen as the functional unit. The reference flow was a car that fulfilled the functional unit. The system boundary included four stages: material production, vehicle production, use, and end-of-life. The impact category was energy consumption. As a result, the energy consumption reduced by 17%, 21%, 25% in the case of (1), (2), and (3) respectively. Therefore we conclude that CFRP is good for reducing environmental burdens of passenger cars, and in addition that the flexible use of CFRP, in accordance with performance that car parts demand, and recycling process are very important. INTRODUCTION Progress of fuel efficiency is strongly needed to reduce environmental burdens in the transport sector. Lightening vehicles is a very important technology that can contribute to easing the burden. In recent years, carbon fiber reinforced plastics (CFRP) have attracted a lot of attention as light materials. As shown in Figure 1, CFRP have such a high specific strength and specific rigidity that we have been using them for airplanes, rockets, etc. Although we strongly need the same benefits in automotive applications, the high price and the difficulty of the recycling process have inhibited its widespread use in the automotive industry, in particular in mass-produced passenger cars. However, in the last few years, the amount of CFRP production has been increasing and much work has been done in developing lower-cost CFRP, which has lead to the improved probability of using CFRP for mass-produced cars. The energy-saving effect of CFRP during the life cycle, however, might be small because CFRP need large energy resources when they are produced. We, thus, used the life cycle assessment (LCA) and calculated how much the environmental burden of conventional steel cars changed when we replaced steel with CFRP whose performance was proper for mass-produced passenger cars. In addition, we use the new energy intensity of CFRP that was recalculated last year [1]. In this LCA, our database of energy intensity was so imperfect that the impact assessment was very difficult. Thus we only carried out an inventory analysis (LCI).