Nope. It's rarely even big enough for a yellow tang (which, of all the tangs, require the least amount of space). Plenty of people keep blue tangs in tanks that size and smaller, but 99.9% of them end up getting ich and spread it to all the other fish in the tank. If that's a risk you are willing to take, then you can try it, but I personally would never put a blue tang in a 55 gallon tank. Or my 240! That's how bad they are for ich, I would never have one period. Doc has one and loves it, but I have never met a person that has owned one that has not had ich problems with them, regardless of the tank size.