Reagent-release hydrogels containing an acid or a base solution were prepared and employed as ion suppliers in isoelectric focusing using short capillaries. In conventional isoelectric focusing techniques using microfluidic channels, complicated liquid manipulations are required, which can decrease analytical performance such as the reproducibility of a focusing position. To develop a rapid and sensitive assay based on microfluidic isoelectric focusing, we previously prepared reagent-release capillaries retaining ampholytes by physical adsorption on the inner surface of a short capillary, which were then applied to isoelectric focusing. In this study, reagent-release hydrogels containing an acid or a base solution were developed for isoelectric focusing using short capillaries in place of the acid and base solutions used in conventional microfluidic isoelectric focusing. The prepared reagent-release hydrogels showed some advantages for isoelectric focusing, e.g., high durability for at least five weeks of storage, easy handling as compared to the conventional solutions, and suppression of hydrodynamic flow in capillaries, which often decreases the reproducibility in capillary isoelectric focusing. The migration behavior of ions from the hydrogels into the capillary and the formation of a pH gradient in isoelectric focusing using the reagent-release hydrogels were investigated, which confirmed that the prepared reagent-release hydrogels could form a similar pH gradient to that obtained with conventional capillary isoelectric focusing using the solutions.