Abstract: Concentration of formaldehyde in its vapour in the air above formaldehyde reagent in a closed container was determined by absorbing the gaseous formaldehyde in the air sample by a definite amount of Na2SO3 solution,and the excess of Na2SO3 was titrated by standard iodine solution using starch as indicator.Only 2 min was required for quantitative absorption of formaldehyde by Na2SO3,achieving to a absorption rate of 98.9%.RSD′s (n=7) values obtained were in the range of 3.2% to 3.8%.A self-made absorption flask was used in the determination.The results obtained by the Na2SO3 absorption-iodimetric titration were checked with the conventional iodometry method,no significant difference between the results of the two methods were found.