Simple technique is required to measure the local swelling degree of hydrogels. Whey protein hydrogels are made stained with Rhodamine B fluorescent dye. Wide-field fluorescence microscopy can quantify the total fluorescence in thick transparent gels. Median fluorescence in hydrogels decreases during swelling as expected in isotropic swelling. 2D spatial information of the dynamic swelling is obtained for the first time in protein hydrogels.