Vegetable tannins give leathers some properties like natural look, firmness, toughness and characteristic colour of themselves. Besides these favourable properties, some of the tannins as mimosa and quebracho which belong to condensed tannins, have some undesirable properties like colour changing and darkening caused by exposure to light for prolonged times. This research aims to increase the lightfastness properties of mimosa and quebracho tanned leathers, by chemical modification of these tannins. For this aim sulphitation, sulpho methylation and novalac synthesis modifications were applied to mimosa and quebracho tannins. Comparative lightfastness test results showed that leathers tanned with sulpho methylated mimosa and quebracho tannins had better fastness to light. Additionally the physical properties of the leathers tanned with modified tannins were investigated to compare with the leathers tanned with standard tannins.