The electrochemical behaviour and corrosion inhibition of mild steel in 0.5M and 1M dilute sulpuric acid by rosemary oil (Rosmarinus officinalis) at ambient temperature was investigated through potentiodynamic polarization test, weight loss techniques analysis and optical microscopy. Results obtained showed the organic compound to be highly effective with a maximum inhibition efficiency of 80.8 % and 87.9% from weight loss and 84.1% and 80.8% from polarization test in the acid test solutions. The adsorption characteristics of the compound obeyed the Langmuir adsorption isotherm while the inhibition mechanism was observed from thermodynamic calculations to be physiochemical. Optical microscopy micrographs confirms the overwhelming influence of the compound on the topography and surface morphology of the steel after exposure.