A study was performed to measure and analyze the gas-side fouling of heat exchanger to cool the exhaust gas from sludge incinerator at ironworks. The incinerator gas passes through inside of the vertical tubes of heat exchanger to preheat the combustion air. This kind of fouling occurs at the entrance region of the heat exchanger and thus the perforated fouling plate was designed to measure the gas-side fouling and to analyze the particulate deposit. As a result of analysis, the particulate deposition rate was influenced by temperature, particulate composition and size and also the deposition patterns were different according to the location of perforated fouling plate. The computational analysis was performed to obtain the deposition rates at the perforated fouling plate and the calculation showed that the deposition rate was varied with the hole size and particulate size. It was proved that the fouling at the entrance region of heat exchanger could be measured by the perforated fouling plate designed in this study.