Stimuli-sensitive hydrogels are responsive to specific variations and change their form when exposed to certain conditions. Especially, pH-sensitive hydrogels are applied in new potential areas due to their swelling and deswelling behaviors. Ionic hydrogels are favorable for drug delivery applications, and fluorescence probes have been employed to analyze drug carriers. In literature, drug delivery studies of hydrogels have been focused on colon (pH=5.5−7.5) targeted drug delivery applications. In this study, we investigated swelling processes of pH-sensitive poly (acrylic acid-co-acrylamide) P(AAc-co-AAm) anionic hydrogels in the presence of 30 vol% AAc for jejunum (pH=7.5−9) (upper part of the small intestine) targeted drug delivery applications. Here, we used in situ steady-state fluorescence (SSF) technique based on the change in fluorescence spectra of the injected aromatic probe pyranine (4sPy) at the molecular level.  According to the change in fluorescence emission intensities of the trapped 4sPy during swelling at various pH values, these anionic hydrogels swelled more and much faster at high pH. Our measurements demonstrated that P(AAc-co-AAm) anionic hydrogels reached the maximum swelling ratio at pH=9. SEM results also showed no extra deformation for these hydrogels swollen at pH=9. Fluorescence and gravimetric results affirmed that when the pH is changed from 2 to 10, diffusion coefficients increased drastically and almost reached saturation at pH=9. The diffusion coefficient for the swelling process was comparable to the diffusion coefficient of drug molecules in a controlled drug delivery system. Our fluorescence results indicated that the 4sPy could be a model probe to monitor the drug carriers in such systems.