The ozonation of landfill leachates in a bubble column was investigated concerning the effect of operating parameters, such as initial organic loading (from 550 to 5500 mg/L dissolved COD), reaction time (from 60 to 360 min) and ozone gas phase concentration (from 19 to 38 mg/L) on treatment efficiency implementing a factorial experimental design. All three parameters tested, as well the second order interaction between initial COD and ozone had a statistically significant, positive impact on COD removal. At increased COD loadings and a maximum ozone concentration of 38 mg/L, COD was the single most important factor affecting both COD and phenols removal. Treatment of the raw leachate (5500 mg/L COD) for 360 min and maximum ozone concentration led to 50% COD removal with a first-order kinetic constant of 2.2 10 -3 min -1 , quantitative elimination of color, phenols and acute ecotoxicity and increase of aerobic biodegradability.