The effect of experimental conditions on the degradation of paraquat in herbicide over gama-TiO2 powder prepared by hydrothermal method (particle size about 6-7 nm, specific surface area - 223.6 m2/g) have been investigated. Experimental results showed that suitable conditions are: time for adsorption equilibrium about 60 minutes, amount of gama-TiO2 per 200 ml herbicide solution with concentration of paraquat 19 mg/l about 0.3g, the pH of solution about 7-8 and the degradation times about 4 hours. In the conditions, the concentrations of paraquat in herbicide after decomposing were lower than threshold (0.9 mg/l). It showed that the promise applications of gama-TiO2 powder in degradation of paraquat as well as other organic pollutants can obtain.