The composite fouling of calcium oxalate monohydrate (COM) and amorphous silica (SiO2) were investigated in a dynamic system under subcooled flow-boiling and a novel but simple continuous evaporation setup to simulate the operation cycle in latter effects of sugar mill evaporators. Simulated solutions with various COM to SiO2 supersaturation (SS) ratios as well as those of pure COM and SiO2 were tested for comparative studies. The results demonstrated that COM fouling resistances began to rise shortly after the experiment started with the highest extent of fouling exhibited at an initial COM concentration of 50 ppm (initial COM SS similar to 2.6). The fouling resistance Of SiO2 (500 ppm) began to rise at a theoretical silica supersaturation level of 5.3. SiO2 fouling involved the deposition of two silica species, that is, dissolved monomeric silica and colloidal silica particles, with colloidal silica particles being more prevalent at SiO2 supersaturation. In the binary systems, the synergistic effect of COM on composite fouling occurred at an intermediate concentration of COM (50 ppm) whereas antagonism was obtained at either low or high COM concentration (20 or 100 ppm). The observed variations in the extent of composite fouling may be partly attributed both to the changes in the magnitude of interfacial energy barrier between the surface of the particle and the wall and to the physical properties of the fouling species such as particle size. Instrumental analysis (SEM-EDS and XRD) was used to investigate structure and composition of scale. The presence of COM and its cementing effect in the composite scale from [COM] = 50 ppm were confirmed.