Selective catalytic reduction of NOx by propane was investigated on Go-Beta to clarify the loaded states of cobalt and their role in catalytic activity. At low ion exchange levels less than 100%, loaded cobalt is highly dispersed, which has a high selectivity for NOx reduction. At ion exchange levels much higher than 100%, Co3O4 appears as identified by Raman spectroscopy, and it contributes to propane oxidation by oxygen and lowers the selectivity especially at high temperatures.