A simple, rapid and sensitive method has been developed for the determination of mercury in Hepatitis-B vaccine samples using electrolyte cathode glow discharge atomic emission spectrometry (ELCAD-AES). This method obviates the need of any sample digestion, except simple dilution followed by analysis of the vaccine samples. Analytical performance of the ELCAD-AES for the inorganic as well as the organic mercury (methyl and thiomersal mercury) in the aqueous solutions is investigated. Biological certified reference materials, Tuna fish-IAEA-350 and Tuna fish-BCR-463 are examined for the applicability of ELCAD-AES to quantify the mercury. These results show an accuracy of between 0.6 to 2.1% with an analytical precision expressed as relative standard deviation (RSD%) of between 3 to 7% based on the multiple measurements on multiple sample loadings. In the absence of any CRM of the vaccine sample, the method has been validated by analyzing the same samples by Cold vapour-AAS and Electrothermal-AAS. Accuracy of the ELCAD results for vaccine samples is determined to be within 2 to 9% at various levels of mercury. Detection limit of the method is found to be 25 ng mL^-1 and the analytical precision is between 2-5%.