The absorption and photoluminescence (PL) spectra of PbSe quantum dots (QDs) with different sizes and doped in organic solvent-hexane are measured by using the transmission electron microscopy (TEM), nearinfrared (NIR) absorption spectroscopy, fluorescence spectroscopy and time- resolved spectroscopy at room temperature. An empirical formula of the first absorption-peak wavelength and PL-peak wavelength varying with the size of QDs are obtained. The PL-lifetimes of PbSe QDs are determined by analyzing transient PL-decay curves. It is shown that the lifetime depends on both the surface defect and the size of QDs. The widest distribution of the lifetime ranges 1.44~11.96 μs, which can be deduced from two extreme conditions, i.e., the PL transition is only a direct interband transition and/or only a defected state transition in the range of particle size used. On the other hand, the PL lifetime is dependent weakly on the size of QDs, it will decrease with the increase of the particel size. As an example, the averaged lifetime is among 7.17~6.72 μs for the QDs diameter in the range of 2.7~5.7 nm.