Hi @VanjaV
How about this expression
dt.AsEnumerable().Where(Function(s) System.Text.RegularExpressions.Regex.IsMatch(s("Column2").ToString,"\d{6}")).Select(Function(a) a).CopyToDataTable

Or
dt.AsEnumerable().Where(Function(s) s("Column2").ToString.Trim.Length.ToString.Equals("6")).Select(Function(a) a).CopyToDataTable

Regards
Sudharsan