Semi-interpenetrating polymer network (semi-IPN) strategy is employed to fabricate uniform microspheres with temperature and pH dual-responsive behavior, which is composed of poly(N-isopropylacrylamide) and poly(acrylic acid) in the presence of N,N-methylenebisacrylamide (MBA) as the cross-linker. The influences of MBA amount (M-m) on the structures and properties of the microspheres are investigated in terms of particle size, surface morphology, pH sensitivity, and thermo-sensitivity with low critical solution temperature in the range M-m = 2.5-15%. Additionally, functional group distributions in the microspheres are probed by titration and employing the Henderson-Hasselbalch equation. The results show that all the properties strongly change depending on M-m. Based on transmission electron microscopy and confocal laser scanning microscopy measurements, and these properties, the M-m-induced changes in the structures of the semi-IPN microspheres are discussed.