We have studied the kinetics of the complex formation of gold(III) complexes, [Au(en)Cl2]+ (dichlorido( ethylendiamine)aurate(III)-ion) [Au(dach)Cl2] (dichloride(1,2-diaminocyclohexane)aurate(III)-ion) and [Au(bipy)Cl2]+ (dichlorido(2,2'-bipyridyl)aurate(III)-ion) with guanosine5'-monophosphate (5'-GMP). It was shown that 5'-GMP have a high affinity for gold(III) complex, which may have important biological implications, since the interactions of Au(III) with DNA are thought to be responsible for the anti-tumor activity. The [Au(bipy)Cl2]+ complex is more reactive than [Au(en)Cl2]+ or [Au(dach)Cl2]+. The activation parameters for all studied reactions suggest an associative substitution mechanism. The cytotoxicity of gold(III) complexes was tested on A549 human lung carcinoma epithelial cell line and was evaluated by cytotoxic (MTT and LDH test) and apoptotic assays. The results showed that all tested gold(III) complexes displayed cytotoxic effect on A549 cells. Among the tested gold (III) complexes, AuBIPY showed the best cytotoxic effects.