A dyad system comprising a lipid membrane-incorporated fullerene derivative with an N,N-dimethylpyrrodinium group (C₆₀-1) and a photoantenna molecule (DiD) did not exhibit the high photodynamic activity expected based on its singlet oxygen generation ability. Comparison with a fullerene derivative with an amide substituent (C₆₀-2) suggested the cause to be that some of the fullerene derivative had been released from the liposomes, partly disrupting the dyad system. The dyad system of C₆₀-2 and DiD exhibited about twice the photodynamic activity toward HeLa cells as that of C₆₀-1 and DiD, due to the suppression of the release of the fullerene derivative from the liposomes. The hydrophobicity/hydrophilicity balance of the substituent in fullerene derivatives was shown to be very important to obtain a dyad system in liposomes characterized by high photodynamic activity.