Thiosulphate leaching of precious metals has been developed as an alternative and non-toxic technique to conventional cyanidation. The aim of this work was to investigate the possibility of leaching gold and silver in ammoniacal thiosulphate solutions on a laboratory scale. Samples used in the experiments were taken from Ovacik gold ore deposit, Bergama, Turkey. The influence of temperature, copper sulphate concentration, ammonia concentration, thiosulphate concentration, sodium sulfite concentration and solid/liquid ratio on gold and silver leaching recoveries were investigated and optimum leaching conditions were determined. At these conditions almost 100% Au and Ag leaching recoveries were achieved.