In some cases of sexual assault that are not reported to judicial authorities within a certain time, it is important to detect and identify seminal stains on laundered fabrics. In this study, we aimed to reveal the effect of the time from staining to laundering on the detectability and identification of seminal stains on laundered clothes. A total of 180 pieces of fabric (four different colours and five different types) were stained with seminal fluids, and three different lag times (12 hours, 1 week and 1 month) from staining to laundering were used. Three different laundering protocols were applied to these fabrics after staining. The built-in camera of the Mobile Multispectral UV-VIS-IR Imaging System (R) was used to take photos (1260 in total) of the stains with seven different wavelength and filter options, and the obtained images were evaluated. The Seratec (R) PSA Semiquant test was used to analyse the presence of prostate-specific antigen (PSA) in the seminal stains laundered after different lag times. We observed that in examining with the forensic light source (FLS) system, the time from staining to laundering affected the detectability of seminal stains on pieces of cloth. The best fluorescence was obtained in the examination of semen-stained fabric with FLS, particularly when the fabric was not laundered for one month after staining. On the other hand, the time from staining to laundering had a more limited effect on PSA test positivity than on the results of the examination with FLS.