A process for production of sulphuric acid comprising condensing sulphuric acid vapour from a gas mixture containing 0.01 to 10 vol. % of H.sub.2SO.sub.4 vapour calculated at complete hydration of SO.sub.3 in the gas to H.sub.2SO.sub.4 and 0 to 50 vol. % of water vapour by cooling of the gas in a sulphuric acid tower, wherein a stream containing NH.sub.3 is added upstream of the tower in an amount corresponding to 0.01-100 ppm NH.sub.3 by vol. in the gas stream at the entry of the tower.