the answer is: maybe
if you are outside of the US, you need to take your family documents to the nearest US Embassy. first you will have to prove that your grandfather transmitted US citizenship to his child (the one that is your parent). Then you must prove that this parent was able to transmit US citizenship to you.
Inside the United States, you should submit N-600 to the nearest district office. supporting documentation will need to demonstrate your grandfather\'s US citizenship, and demonstrate that your grandfather transmitted citizenship to your parent (his child) was a US citizen and that your parent transmitted US citizenship to you.
simplest is for your parent (his child) to go to the nearest US Embassy (or district office, if in the US) with grandparent\'s documentation to demonstrate citizenship. If your parent cannot demonstrate US citizenship, you will have to become permanent resident and naturalize on your own.
