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Steady-state and nanosecond time-resolved spectroscopies are performed to investigate the interaction between CdSe quantum dots (QDs) and mesotetraphenylporphyrin (TPP) photosensitizers under two-photon excitation with femtosecond laser pulses. The luminescent intensity and lifetime of the QDs decrease intensively in the QD-porphyrin mixture, whereas those of the TPP increase, suggesting occurence of a nonradiative fluorescence resonance energy transfer (FRET) process between the excited states of the donors and acceptors. An energy transfer efficiency of 0.27 is estimated from quenching of the excited-state radiative lifetime of the QDs. A red shift in the emission spectrum of the CdSe QDs is observed after mixing with TPP, which is speculated to be caused by the energy transfer from QDs of small size to large. This study could be valuable for developing a QD-based drug system for …