When I wipe after I urinate I see blood on my tissue, but see no blood in my urnine.
What could it be?

Assuming you are a woman of childbearing age, it is often just a little menstrual spotting, but if you see it every time you urinate, day in and day out, then see a doctor, and don't urinate before you go so you can give a sample. It isn't necessarily serious and sometimes a diagnosis can't be found without a lot of tests, such as a small kidney stone that may not be evident for years.