Raman spectroscopy was used to elucidate structural changes of wet blue sheep leather due to the growth of fungi belonging to the genus Penicillium. After chrome tanning while leathers are still wet, they are prone to be affected by Penicillium, resulting in degradation of leather structure. In this study, different fungi species -Penicillium glabrum, Penicillium commune, Penicillium echinilatum, Penicillium brevicompactum and Penicillium chrysogenum- were inoculated on wet blues and let grown for 14 months. After 14 months, changes on wet blue structure were investigated with Raman spectroscopy. The results showed that chrome-tanned sheep leathers are affected to different degrees by various fungi from the Penicillium.