Simple, rapid and precise determination of free sulfuric acid in unstabilized cellulose nitrate is accomplished by dissolving in 90 % v/v acetone-water solution and subsequent titration of sulfate by the lead nitrate-dithizone titration method.. The method is; proved accurately and sensitively for tracing very small amounts of free sulfuric acid present in all types of unstabilized cellulose nitrates. One mom advantage of the method is that free nitric acid do not interfere in the determination, and, hence, there is no need to estimate its value and to correct the value for the free sulfuric acid content; the determination of free nitric acid, which is likely to be present with sulfuric acid in unstabilized cellulose nitrate is a very difficult problem.