The corrosion inhibition effect of environmentally friendly organic admixture of Rosmarinus officinalis and 5-bromovanillin on 1018 carbon steel in 1 M HCl and H2SO4 solution was assessed through potentiodynamic polarization, coupon measurement, optical microscopy and ATF-FTIR spectroscopy. Experimental data show that the compound performed more effectively in HCl solution with maximum inhibition efficiency 92.57 and 94% in comparison with 64.57 and 64.55% in H2SO4 from electrochemical analysis due to film formation and chemisorption adsorption of the compound. Functional groups of amines, amides, H–bonded alcohols and phenols, C-H stretch alkanes, alkynes and C-C stretch in-ring aromatics identified through ATF-FTIR spectroscopy completely adsorbed on the steel surface in HCl, but partially in H2SO4 as shown in the decreased peak intensity. Thermodynamic calculations showed the cationic adsorption to be through chemisorption and physiochemical mechanism according to Langmuir, Freundlich and Temkin adsorption isotherms. Images from optical microscopy showed a well-protected surface morphology of the inhibited steel in comparison with images from the corroded stainless steel. Severe surface deterioration and macropits were observed in the uninhibited samples. The inhibition property of the organic compound was determined to be mixed type.