The amount that we get as per diem allowance in us is non taxable in us, if this amount anyone takes back to india, is it taxable there or not.

Per diem, by definition, is a set reimbursement amount for daily expenses.

If you get per diem under an "accountable" plan (meaning that you submit an expense report and the expenses EXCEED the amount of per diem received), said per diem is NOT TAXABLE and does not have to be reported.

However, if you get the per diem under a "non-accountable" plan (no expense report is required), then the per diem IS subject to U.S. and state income taxes. You CAN deduct the actual expenses incurred as an itemized employee business expense, but Alternative Minimum Tax will kick in after the expense hits a certain level.

The U.S. is somewhat unique in this treatment of per diem. In most other countries, per diem is NOT taxable.

I suspect that India has the same policy, but I am NOT sure.