Due to the some chemical substances used in leather manufacturing, free formaldehyde is released in finished leathers and made serious problems for tanners. This situation causes the firms not to get Eco-Leather label and great problems are experienced about leather sales especially in recent years because natural and ecological products are in fashion. This study aims to reduce the free formaldehyde amount in leather by using various plant extracts (hazelnut shells, thyme, olive shoots, lavandula, ivy, christ's thorn seed), which are obtained from agricultural wastes, during rearming stage of leather processing. The analyses have been conducted with HPLC device according to IUC 19 (ISO TS 17226) method. According to the results; the extracts from hazelnut shells, thyme and olive shoots reduced the free formaldehyde amount on the leather by 35.49%, 33.86%, and 24.03% respectively. Color measurements on all finished leathers have been conducted with Konica Minolta CM-3600d brand spectrophotometer, light fastness analyses with ATLAS-XENOTEST ALPHA+ test instrument and according to ISO 105-B02 standard's method. The results showed that the plant extracts impacting formaldehyde considerably also improved the light fastness of the leather samples for a certain extent.