In this investigation photocatalytic degradation of basic blue 9 or methylene blue (MB) as color pollutants was studied. Cobalt sulfide was supported on AlMCM-41 material using ion-exchange method. The results show that CoS/AlMCM-41 is an active photocatalyst. The catalyst is characterized by X-ray diffraction (XRD) UV–vis diffused reflectance spectra (UV–vis DRS) and scanning electron microscopy (SEM) techniques. The maximum effect of photodegradation was observed at 7wt% CoS/AlMCM-41. Pseudo-first order reaction with k=0.032 was observed for the photocatalytic degradation reaction. The effect of some parameters such as pH, amount of photocatalyst and initial concentration of dye were also examined. The effect of dosage of photocatalyst was studied in the range 0.04–1.2g/L. It was seen that 0.8g/L of photocatalyst is an optimum value for the dosage of photocatalyst. In the best conditions, the degradation efficiency was obtained 0.32ppm for MB dye.