The performance of two laboratory-scale fluidized bed reactors with natural zeolite as support material when treating high-strength distillery wastewater was assessed. Two sets of experiments were carried out. In the first experimental set, the influences of the organic loading rate (OLR), the fluidization level (FL) and the particle diameter of the natural zeolite (Dp) were evaluated. This experimental set was carried out at an OLR from 2 to 5g COD (chemical oxygen demand)/Id, at FL 20% and 40% and with Dp in the range of 0.2-0.5 mm (reactor 1) and of 0.5-0.8 mm (reactor 2). It was demonstrated that OLR and FL had a slight influence on COD removal, whereas they had a strong influence on the methane production rate. The COD removal was slightly higher for the highest particle diameter used. The second experimental set was carried out at an OLR from 3 to 20 g COD/I d with 25 % of fluidization and Dp in the above-mentioned ranges for reactors I and 2. The performance of the two reactors was similar; no significant differences were found. The COD removal efficiency correlated with the OLR based on a straight line. COD removal efficiencies higher than. 80% were achieved in both reactors without significant differences. In addition, a straight line equation with a slope of 1.74 d- 1 and an intercept on the y-axis equal to zero described satisfactorily the effect of the influent COD on the COD removal rate. It was also observed that both COD removal rate and methane production (Qm) increased linearly with the OLR, independently of the Dp used.