Msdn tells default isolation mode is database dependent. (2023 documentation does too, and has much better code examples.)

It also supply an example of how to handle transactions, which is what you need to benefit from what you likely want with isolation mode repeatable read . Beware, their example has a serious flaw, as it will swallow any exception.

Here is a fixed version of their example. context is supposed to be an instance of a class derived from DBContext .

using (var dbContextTransaction =
    context.Database.BeginTransaction(IsolationLevel.RepeatableRead))
{
    try
    {
        // Your work here, then

        context.SaveChanges();
        dbContextTransaction.Commit();
    }
    catch
    {
        dbContextTransaction.Rollback();
        throw;
    }
}

As warned by Panagiotis Kanavos, this kind of locking should be avoided as much as possible. It reduces scalability, increases dead locks risks, may completely blocks other users as long as the transaction is running, ...

The try catch rollback could be considered superfluous, as disposing an ongoing DbTransaction causes it to rollback (and the using will ensures it gets disposed).