I have a string something like, string str = "(50%silicon +20%!(20%Gold + 80%Silver)| + 30%Alumnium)"; I need a Regular Expression which would Replace the contents in between ! and | with an empty string. The result should be (50%silicon +20% + 30%Alumnium). If the string contains something like (with nested delimiters): string str = "(50%silicon +20%!(80%Gold + 80%Silver + 20%!(20%Iron + 80%Silver)|)| + 30%Alumnium)"; The result should be (50%silicon +20% + 30%Alumnium) - ignoring the nested delimiters. I've tried the following Regex, but it doesn't ignore the nesting: Regex.Replace(str , @"!.+?\|", "", RegexOptions.IgnoreCase);