I want to create the regular expression in javascript which will check the valid conditional string like -1 OR (1 AND 2) AND 1 -1 OR (1 AND 2) -1 OR 2 -1 OR 1 OR 1 -1 AND 1 AND 1 The string should not contain 'AND' and 'OR'. For example - 1 OR 2 AND 3 is invalid. -It should be (1 OR 2) AND 3 or 1 or (2 AND 3). I tried the following Regex. It works for most of the conditions but it is failing to check the above condition. /^(\s*\(\d+\s(AND|OR)\s\d+\)|\s*\d+)((\s*(AND|OR)\s*)(\(\d+\s(AND|OR)\s\d+\)|\s*\d+))*$/ Can anyone please help me to sort out the above problem.