The present invention provides a method for obtaining high purity chlorosilanes from chlorosilanes containing boron impurities and phosphorus impurities. On the basis of the finding that solid by-product formation in the purification of chlorosilanes by adding an aromatic aldehyde results from a catalytic reaction by iron ions or rust-like iron, a Lewis base having a masking effect is added to chlorosilanes. Examples of the Lewis base include a divalent sulfur-containing compound and an alkoxysilane. The divalent sulfur-containing compound is preferably a compound represented by the formula: R—S—R′ (wherein R is a hydrocarbon group or a carbonyl group; and the sum of the carbon atoms in R and R′ is 7 or more), and the alkoxysilane is preferably a compound represented by the formula: RxSi(OR′)4-x (wherein R and R′ are each an alkyl group having 1 to 20 carbon atoms).