We have investigated CdSe quantum dots (QDs) by micro photoluminescence (PL). To reduce the number of QDs to be observed, Al masks with sub-micron size apertures are deposited on the sample surfaces, which make it possible to repeatedly trace the same excitation position in taking temperature dependent micro-PL spectra. Resolved sharp lines having linewidth similar to 500 mu eV are observed. The results of temperature dependence reveal that the linewidths of QDs broaden with increasing temperature, which is considered to come from lifetime broadening of ground state by absorption of phonons. The linewidth broadening depends on the peak energy position of the QDs. The linewidths of lower-energy lines corresponding to larger size QDs, are more temperature-dependent than those of higher-energy lines corresponding to smaller ones. The different linewidth broadening can be qualitatively explained by taking into consideration of different energy level spacing between discrete states of the QDs.