Two polyurethane based triblock copolymers, namely, poly(N-isopropylacrylamide)-b-polyurethane-b-poly(N-isopropylacrylamide) (PIA-PU-PIA) and poly(tert-butylacrylate)-b-polyurethane-b-poly(tert-butylacrylate) (PtBA-PU-PtBA), were synthesized via atom transfer radical polymerization (ATRP) mechanism and characterized. The inhibition potentials of the polymers on mild steel corrosion in 0.5 M H2SO4 were studied using electrochemical, scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques. The results obtained from potentiodynamic polarization studies showed that the two polymers are mixed-type inhibitors and exhibit passivating activities. The adsorption of PIA-PU-PIA on mild steel surface obeys the Langmuir adsorption isotherm, while that of PtBA-PU-PtBA obeys the El-Awady isotherm. The two polymers adsorb on the mild steel surface via competitive physisorption and chemisorption mechanisms. Both SEM and AFM analyses confirmed the formation of protective layers of the inhibitor molecules on the steel surface. The results obtained showed that PIA-PU-PIA exhibited higher inhibition performance than PtBA-PU-PtBA, and the trend was corroborated by the results obtained from quantum chemical calculations.