Bulk heterojunction-type organic photovoltaic (OPV) cells have attracted attention because of their light weight, flexibility and solution-process construction. In our ongoing work in preparing a series of the PCBM analogues, we prepared Methyl-C61-phenyl carboxylic acid methyl ester (MPCM) as well as its C70derivatives and fabricated OPV devices with poly(3-hexylthiophene) (P3HT) as the donor. The performance of devices with [60]MPCM and [70]MPCM was compared, [70]MPCM showing a higher PCE than [60]MPCM. However, because of the high aggregated property of MPCM, the OPV device performance using MPCM and P3HT gave often morphology problem; thus we also prepared new fullerene derivatives with an alkyl spacer as the modification of MPCM and fabricated OPV devices with P3HT as the donor. The performance of OPV devices of these fullerene derivatives with an alkyl spacer was investigated, some of them showing higher PCE than that of PCBM. Furthermore, we synthesized novel fullerene derivatives with different carboxylic acid esters, e.g., hexyl ester; methyl-C61-phenyl carboxylic acid hexyl ester (MPCH). These derivatives have the merit of higher solubility because of the long alkyl chain. Organic photovoltaic devices were fabricated using these fullerene derivatives as an electron acceptor and P3HT as an electron donor. MPCH showed PCE that is higher than that of PCBM. Figure 1