Iron concentrations of composite coagulant powders were measured by means of the photoacoustic effect. The onset of photoacoustic signal saturation for iron in the powders was 5 wt. %. This problem was solved by adding one of the components of the composite coagulant as a diluent to the samples. Based on the findings of this research, photoacoustic response of composite coagulant is closely correlated to iron concentration in the coagulant powders. Photoacoustic signal was found to be a function of excitation power of photoacoustic set-up. Sample grinding helps improve the accuracy of photoacoustic measurement of iron in composite coagulant.