In this study*, it was aimed to observe, genotoxic effects of antituberculosis drugs and combinations on rats. Animals were treated with 31.5 mg/kg isoniazid (INH), 54 mg/kg rifampicin (RIF), 189 mg/kg pyrazinamide (PYR), 100 mg/kg ethambutol (ETA), INH + RIF + PYR (MIX1) and INH + RIF + PYR + ETA (MIX2) mixtures applied via gavage for 90 days. At the end of the study, blood, liver and kidney samples were taken and evaluated by Comet and Micronucleus techniques. Compared to control group, head intensity decreased, tail intensity and tail migration increased on experiment groups in blood samples. Head intensity of PYR and mixture groups decreased, tail intensity of PYR and mixture groups increased and tail migration of PYR, ETA and mixture groups increased in liver samples. Head intensity decreased and tail intensity increased of INH, RIF, ETA and MIX1 group; tail migration increased of MIX1 group in kidney samples. Compared to control group, micronucleus rate of ETA, RIF and MIX 2 groups increased in experiment groups. In conclusion antituberculosis drugs and their mixtures applied for 90 days causes to double strand break of DNA damage at different degrees in blood, kidney and liver cells in rats.