Fouling on heat exchanger surface is a severe problem in food industry. This study investigated the fouling and cleaning behaviors of soy protein isolates (SPI) in heat exchangers, using a previously established real-time monitoring laboratory system. SPI fouling deposit was formed at different surface temperatures of 80, 85 and 90°C. For cleaning, the effect of the NaOH concentration was investigated. The fouling and cleaning behaviors of whey protein concentrate (WPC) were studied for a qualitative comparison. The two solution concentrations were kept at 6 wt%. Under the constant heat flux condition applied in the experiments, increasing the surface temperature significantly increased the fouling rate of SPI. SPI deposit was much easier to remove compared to WPC deposit. Visualization showed that the cleaning behavior of SPI was different from that of WPC in that it swelled rather quickly followed by the species seeping out from the swollen structure.