E FFECTS of ageing on the optical properties of CR-39 SSNTDs were investigated for two stored types. The optical band gap of the stored pristine was roughly the same as the new pristine samples before chemical etching. Energy gaps were found to decrease with the chemical etching. The onset of the transmittance spectra of the CR-39 SSNTDs were measured at 240 nm and 300 nm for 26 y and 10 y respectively. The etch pit diameters of α−particles were deceased with the storage period while the rate of the decrease depended markedly on the storage conditions. The fading effects of tracks due to radon exposure were a little bit changed. The storage at the temperature of 4 °C for 26 y did not bring any significant changes to the detection efficiency. These characterizations of the response of CR-39 SSNTDs to alpha particle were essential for the storage under certain conditions.