Experimental studies were carried out on the separation of unburned carbon in fly ash powder using a special louver separator. The optimum operating conditions and the effects of the inlet flow rectifier, blade shape, and number of separators on both the separation performance and unburned carbon content were examined. Fly ash powder with a median size of about 44.7 mu m and average unburned carbon content of about 20.9% was used as the feed powder. The study showed that there was an optimum velocity corresponding to the best separation performance in terms of the particle size and unburned carbon content. It was found that a louver separator with an inlet rectifier and additional inclined wall shows better separation performance and unburned carbon content separation compared to a conventional separator. When a special blade was used, the separation performance improved in comparison to typical flat blade. The separation performance and unburned carbon content of two louver separators connected in series were better than those of a single separator. In the case of two louver separators, the unburned carbon content of the fine side was reduced to as low as 8% while about 78% of carbon yield was achieved; therefore it is recommended the use of two special louver separators connected in series. A model of louver separator, based on the unburned carbon profile of feed powders and the data of partial separation efficiency was developed and the calculated results were compared to the experimental results. Calculated result by using the model showed qualitative agreement with the experimental results, and the optimum operating conditions required to maximize the unburned carbon separation were determined.