A bench-scale model of a partially packed upflow anaerobic fixed film (UAF) reactor was set up and operated at five different hydraulic retention times (HRTs) of (17, 14, 10, 8, and 5) days. The reactor was fed with synthetic rubber wastewater consisting of a chemical oxygen demand (COD) concentration of 6355-6735 mg/L. The results were analyzed using the Monod model, the Modified Stover-Kincannon models, and the Grau Second-Order Model. The Grau Second-Order model was found to best fit the experimental data. The biokinetic constant values, namely the growth yield coefficient (Y) and the endogenous coefficient (K d ) were 0.027 g VSS/g COD and 0.1705 d À1 , respectively. The half-saturation constant (K s ) and maximum substrate utilization rate (K) returned values of 84.1 mg/L and 0.371 d À1 , respectively, whereas the maximum specific growth rate of the microorganism (μ max ) was 0.011 d À1 . The constants, U max and K B, of the Stover-Kincannon model produced values of 6.57 g/L/ d and 6.31 g/L/d, respectively. Meanwhile, the average second-order substrate removal rate, k s(2) , was 105 d À1 . These models gave high correlation coefficients with the value of R 2 ¼ 80-99% and these indicated that these models can be used in designing UAF reactor consequently predicting the behaviour of the reactor.