If you're using the xsd.exe tool to generate C# code from an XML Schema you'll find that an attribute defined as an integer is generated into a string field.

The reason is listed on MSDN:

The xs:integer type is specified as a number with no upper or lower bound on its size. For this reason, neither XML serialization nor validation map it to the System.Int32 type. Instead, XML serialization maps the xs:integer to a string while validation maps it to the Decimal type that is much larger than any of the integer types in the .NET Framework.