Inhibition of mild steel corrosion in 3% sodium chlroide solution by sodium tripolyphosphate (STPP), sodium hexametaphosphate (SHMP) amd adenosine triphosphate (ATP) in presence of 200 ppm zinc acetate has been investigated using weight loss, electrochemical polarisation and scanning electron microscopy techniques. Various corrosion parameters such as Tafel slopes, corrosion current density, heat of absorption and activation energy value have been calculated to understand the inhibition mechanism. Inhibition efficiency increased with increase in concentration for STPP and SHMP whereas it decreased for ATP. However, inhibition efficiency decreased for all the three phosphates with increase in temperature. All the three phosphates acted as mixed inhibitors though anodic reactions are suppressed more in comparison to the cathodic reactions. STPP acted through chemisorption whereas SHMP and ATP are physically absorbed over the surface of mild steel.