Do we have any blood relation?

Question

He is from my mother's side. My grandma's sister is his mother. Do we have any blood relation???

Answer 1

Yes, you have the same great-grandparents.  You are second cousins.  

Answer 2

If he is the son of your grandmother's sister, your grandmother would be his aunt.  He would be a cousin of your mother, and a second cousin to you.  He would not be your uncle, unless you have some really odd family relationships.  To be your uncle, he'd have to be a brother of your mom or dad.  In terms of genetic relationship, you probably don't have any shared genetic material, at best you would share very little.  You would be much more likely to be genetically related if you were both boys, related through your fathers.