The optical response of colloidal photoluminescent (PL) semiconductor nanocrystals to 137 Cs y radiation was investigated. The quantum dots (QDs) used were CdSe dispersed in hexane, exhibiting bandgap absorption and emission peaking at 556 nm and 563 nm, respectively. The doses of the 137 Cs y radiations were 0.1, 1.0, 10 and 100 Gy with a dose rate of 0.805 Gy/min. Each radiation was performed on two identical samples; right after the radiation, absorption and emission measurements were performed. The change of the optical properties after the radiation was presented together with those of a control sample without radiation exposure. The prompt absorption measurements showed that there is little change with the 0.1 Gy up to 100 Gy radiations, while the prompt emission measurements showed that with the 0.1 Gy and 1 Gy radiation, there is a negligible change in the PL intensity; with the 10 Gy and 100 Gy radiation, there is a noticeable decrease in the PL intensity. Therefore, it seems that the radiation does not destroy the QDs themselves but leads to some loss of their surface passivation. Furthermore, the optical properties of the eight irradiated samples and the control sample were monitored periodically up to days. Interestingly, after the storage of days in dark, there is significant recovery in the PL intensity of the large-dose irradiated samples; such a rebound tendency provides the potential for the colloidal QDs to be novel and promising candidates in radiation dosimeter with multi-detection capability.