To review the relevance of sialic acid as a tumour marker in oral cancer. Tumour marker are useful in the screening for early malignancy. Sialic acids are important in determining the surface properties of cells and has been implicated in cellular invasiveness, adhesiveness, and immunogenicity. Sialic acids are commonly found at the outermost end of glycan chains of all cell types. Increase in the levels of sialic acid in oral cancer indicates its importance as a tumour marker.Both serum and salivary sialic acid levels can be used as a screening tool and a diagnostic aid for oral cancer. Salivary sialic acid can be used as a non-invasive, cost effective and reliable diagnostic methods for screening and monitoring of oral cancer. In patients with oral cancer, glycoprotein metabolism is altered. Increase in the levels of sialic acid in oral cancer indicate its importance as a tumour marker. Changes in the serum is reflected in saliva. Salivary sialic acid can be used as non-invasive, cost effective and reliable diagnostic methods for screening and monitoring of oral cancer. Early the diagnosis, better the prognosis.