I need to give 500 dollars cash as gift to my foreign business partner when he travels to the US, so that he will keep doing business with me.
I am wondering how can I deduct this 500 dollars cash from my company's profit for tax purpose. Because I can NOT ask him to write a receipt stating he gets 500 dollars from me.

Without getting into the issue of ethics or legality concerning bribes to your business partner - you can deduct gifts to business associates up to $25 without any issue. You can not deduct gifts that exceed $25. The fact that your partner won't give you a receipt is immaterial.

One way around it is if the gift is associated with "entertainment" - such as tickets to a concert or ball game - you can classify it as an entertainment expense, which is not limited to the $25 limit.

Thank you !
Just to clarify your point, for example: If I buy a leather bag for 500 dollars with a receipt and give it to my business associate, I still can NOT deduct it be cause it is more than 25 dollars ?

Thank you !
Just to clarify your point, for example: If I buy a leather bag for 500 dollars with a receipt and give it to my business associate, I still can NOT deduct it be cause it is more than 25 dollars ?

Correct.