Silver nitrate (AgNO 3 ) was used as a mordant for dyeing cotton fabric with natural dyes. Due to the high concentrations of catechin and tannin, green tea was used as a natural dye. The green tea extraction was performed under neutral and alkaline conditions. Four molar concentrations of AgNO 3 were used, namely 1, 5, 10 and 50 mM. Mordanting was performed during dyeing with green tea extracts. The colour (CIE L*a*b* values) and UV protection factor (UPF) of the dyed cotton samples before and after ten repetitive washings were measured spectrophotometrically. The results revealed that with the increase of the molar concentration of AgNO 3 , the samples became darker, redder and bluer. Dyeing with alkaline green tea extract was not as successful as dyeing with neutral green tea extract. Diff erent shades of cotton were achieved when dyeing with neutral green tea extract and mordanting with diff erent molar concentrations of AgNO 3 . Using 50 mM AgNO 3 achieved a very dark grey (almost black) colour. Cotton samples dyed with neutral green tea extract had excellent UV protective properties (50+), some even after washing. Keywords: dyeing, green tea, mordanting, silver nitrate, colours, UV protection. Tekstilec, 2015, letn. 58(3), str. 191-198 Izvleček Pri barvanju bombažne tkanine z naravnim barvilom je bil kot čimža uporabljen srebrov nitrat (AgNO 3 ). Kot naravno barvilo je bil uporabljen zeleni čaj, saj ima visoko vsebnost katehina in čreslovine.