Clearly understanding of swelling kinetics and erosion behavior of polymer can reveal drug release mechanism and kinetics. Recently, swelling progression and mobility of water molecule inside polymers have been investigated by several technologies, including magnetic resonance imaging (MRI), X-ray microtomography (XμT), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), fluorescent, texture analyzer, and ultrasound techniques. Each technique offers its own advantages which suit to different study purposes. This review describes application of the advanced technologies to monitor swelling–erosion behaviors and also compares pros and cons of each technique. This may help the researchers to select the appropriate technique for their polymer.