Full factorial experimental design technique was used to study the main effects and the interaction effects between operational parameters in the photocatalytic degradation of oxalic acid in a batch photo-reactor using TiO2 aqueous suspension. The important parameters which affect the removal efficiency of oxalic acid such as agitation, initial concentration, volume of the solution and TiO2 dosage were investigated. The parameters were coded as X1, X2, X3 and X4, consecutively, and were investigated at two levels (−1 and +1). The effects of individual variables and their interaction effects for dependent variables, namely, photocatalytic degradation efficiency (%) were determined. From the statistical analysis, the most effective parameters in the photocatalytic degradation efficiency were initial concentration and volume of solution. The interaction between initial concentration, volume of solution and TiO2 dosage was the most influencing interaction. However, the interaction between agitation, initial concentration and volume of solution was the least influencing parameter.