Polyethylene imine (PEI) microgels prepared via micro emulsion polymerization technique were treated with 1,3-propane sultone to obtained betainized PEI (b-PEI) microgels. The betainization reaction generated zwitterions on PEI microgel that are positive charges from quartemized amine groups of PEI, and the newly formed negative charges from SO3- groups from the modifying agent, 1,3-propane sultone offered interesting properties. The smaller size of b-PEI microgels that are obtained by simple filtration were increased with betainization from 512 +/- 14 to 1114 +/- 86 nm. Also, the betainization of PEI microgel provided negative zeta potential values at high pH values as 9, 10, 11, and 12. Moreover, the b-PEI microgels render more effective dye absorption capabilities for anionic or cationic organic dyes such as Methyl Orange (MO) and Methylene Blue (MB) separately with the significant increase dye adsorption capacity of 354 +/- 31 and 274 +/- 19 mg/g respectively. Moreover, antibacterial properties of b-PEI microgels tested on the E. coli ATCC 8739 and S. aureus ATCC 6538 were diminished whereas bare PEI has low MIC and MBC values (strong antibacterial properties). Interestingly, the PEI microgels known for their strong antibacterial and toxic nature found to be biocompatible upon betainization reaction. The biocompatibility test were carried with WST-1 tests and double staining methods. The cytotoxicity, apoptotic and necrotic cell tests were shown that PEI microgels induce no cytotoxicity up to 400 mu g/mL whereas PEI microgels possessed 50% toxicity at this concentration, suggesting that b-PEI microgels become biocompatible upon betainization with, 3-propane sultone. (C) 2017 Elsevier B.V. All rights reserved.