Background & Objectives: Increasing water resources pollution by heavy metals cause serious environmental and health concerns in the world. Selenium blood levels of >100 𝜇g/dl can result in selenosis. Atomic absorption spectroscopy is the most common method for selenium detection. This technique has several disadvantages such as high equipment and operational costs, time-consuming and the need for quality control of the test method. Methods: In this study, the HMS) Hexagonal mesoporous silica (activated by 4- (2-pyridylazo)-resorcinol (PAR) was used for spectrophotometric determination of selenium. The qualitative detection was done by colour change of sediment from orange to pink in water samples and the quantitative detection by a spectrophotometer. Various parameters such as pH, the initial concentration of the selenium, contact time, and the indicator doses were also examined. Results: The results of this study showed that the qualitative and quantitative detection of selenium are better done with increasing the contact time. The best condition for selenium detection was observed at pH =10. Increasing the indicator doses had no significant effect on the identification process. Increasing initial concentration of selenium increased the pink colour formation and consequently enhanced accuracy of qualitative and quantitative detection. This study is a basic and applied research. Conclusion: The HMS sensor activated by 4- (2-pyridylazo)-resorcinol (PAR) can be used as an inexpensive and rapid indicator for quantitative (spectrophotometry) and qualitative (colour change) detection of selenium in water and wastewater in research and administrative unites.