Calcium alginate microparticles alone are not suitable for sustained oral drug delivery applications. They rapidly disintegrate in weakly alkaline conditions of intestinal fluid and liberate their content. Herein, sodium alginate was chemically modified to circumvent this problem. The oxidation of the polymer was controlled such that oxidized alginate could form microparticles by ionic gelation with divalent Ca+2 ions. Oxidized polymer was characterized by measuring the aldehyde content, degree of oxidation and by FTIR spectroscopy. Spherical oxidized alginate particles were able to control the release of flurbiprofen in simulated gastrointestinal milieu for longer durations. The drug release correlated with the swelling nature of particles. In addition, ibuprofen-loaded Ca-alginate particles reinforced with cationic polyelectrolytes exhibited sustained drug release properties. The percentage drug release was very small in gastric fluid and thus could avoid gastric side effects associated with the use of non-steroidal anti-inflammatory drugs (NSAIDs). This book was written for the benefits of the research scholars and scientists working in the field of drug delivery research.