Is this constant? A large quantity of blood?
Straining to urinate or urinating more or less often? More or less quantity?
Any other symptoms? When did this start?
Thanks for replying back so quickly. This is likely caused by a urinary tract infection, possibly with crystals or even stones developed.
The situation is much different with a male cat than with a dog or even female cat when this occurs. That is because the male cat's urethra is extremely thin, and what usually causes this is a urinary tract infection with crystals, and the crystals get stuck in the urethra and block the bladder from emptying.
This is a dire emergency situation, requiring an emergency vet asap. It is lethal if not treated quickly- as the bladder continues to fill with urine and will eventually rupture. It is painful for the cat, even at this point. If you call your vet now, there should be a recording telling you where the nearest emergency hospital is, and your local yellow pages can be of help as well. Unfortunately there is nothing you can do at home: the only way to clear this is by having the cat sedated, catheterized, and professionally "flushed" to get this unblocked; then the catheter needs to remain in place while the crystals are treated and dissolved so the cat can urinate on his own again.
It is not uncommon for this to happen with male cats; but often a different, prescription diet is necessary if it keeps happening, as this will keep the urine pH at a level not livable by these crystals.
If needing financial assistance for an emergency vet, you can apply for care credit at the office, a low to no interest credit card for situations like this; the vet can be working on your animal in no time- acceptance takes just minutes.
Best of luck!!!