Need to bring $50,000 cash into US. Was given as a gift from non US citizen/resident family member. Can I bring it into US, pay no tax and use it to pay as down payment for a house? How do I prove that it was a gift from family member outside the US? Thanks!

I believe you can bring in 10K without too many questions. However, you will need to declare anything above that. There is no reason for YOU to pay taxes on the gift money. The giftor might but not the giftee. Depositing that much cash will make the bank report the income.

How do I prove that it was a gift from another country? The bank will report it and then what?
Thanks for your help!

Bring a notarized letter stating this is a gift. Large cash deposits are reported to the fed in an effort to track terrorist and drug money. That's why drug money is always lees than 10K. With sufficient backup you shouldn't have an issue. By the way, from what county are you trying to bring the money?

The gift is from Russia. So, if I deposit less than 10k each time, then I do not need any proof that it was a gift? Or is it just 10k per year? Thanks!

Anyone can give you money. In the US, the person giving the money is limited to $12K (?) without paying taxes. I'm not sure about Russian laws. You can receive $50K but just depositing or transferring that amount of miney will raise some eyebrows, particularly at the bank where deposited. They will report it to the IRS. You may have to explain it or better yet, go to the IRS website and post a question. They will have a more definitive answer than we can offer.