Mesoporous silica has been widely studied as promising carriers in drug delivery systems due to their properties, which allow loading of significant amount of drugs and can solve problems related with low solubility and instability of biologically active compounds. In this study in situ (direct synthesis) and post-synthesis (incipient wetness impregnation and template ion-exchange) techniques were applied to modify MCM-41 mesoporous silica with Mg. Various characterization techniques were used to completely investigate the influence of the modification procedure on physicochemical properties of the obtained carriers. Kaempferol, a polyphenol antioxidant with many beneficial effects on human health, was loaded by incipient wetness impregnation on parent and Mg-modified MCM-41 carriers. The results from the release experiments in buffers with pH 1.2 and 6.8 show improved solubility of kaempferol from obtained formulations in comparison with pure polyphenol. Therefore, development of delivery systems on the basis of mesoporous silica carriers can improve the kaempferol bioavailability and thus to enhance the effect of the antioxidant activity of the drug.