In different circumstances either may be correct. I cannot enter the theatre, I don't have a ticket. 'I would like to buy 3 tickets for the concert'. 'Sorry. I don't have any tickets'. In normal situations you would expect the 'I' to indicate a single ticket - then 'I do/don't have a ticket'

Of course 'ticket' is a countable noun. One ticket, two tickets, three tickets! There is no great philosophical mystery about countable and uncountable nouns: if you are using a word in a plural form (tickets, apples, children) then that word is obviously countable. Likewise, if you can put it with 'a' (which means 'one') it is also countable. One ticket. It really is that simple. As for your questions, both are correct, but the context might be different. 1. If you are on a train, the inspector might ask to see your ticket. Here you would say 'I don't have a ticket'. 2. Let's say that students at your college are selling tickets for a concert at the college. One of your friends mistakenly believes that you are one of the people who are selling tickets. He asks you for a ticket, and you answer: 'I don't have any tickets.'. Can you see the difference? In #1, the expectation is that you will have one ticket, so you answer 'I don't have a ticket'. In #2, the expectation is that you will have a lot of tickets, so you answer 'I don't have any tickets'. This has NOTHING to do with countable or uncountable nouns. It's to do with the expectation of how many you will have - one or many. The uncountable/countable issue is simply a way of describing the grammar: There is some tea / There isn't any tea (uncountable) There is a ticket / There isn't a ticket (singular) There are some tickets / There aren't any tickets (plural) Here's a simple checklist: Is it plural? Yes? Then it's countable. eg 'some tickets' 'any tickets' '3 tickets' Does it have the word 'a' or 'a' or 'one' before it? Yes? Then it's a singular countable noun eg a 'ticket' Is it a singular noun preceded by 'any' or 'some'? Yes? Then it's uncountable eg some tea, any tea, any luck, some money. Native English speakers don't need to learn about uncountables or countables as a concept, because we instinctively use the correct grammar by copying what others say. And that's what you should do.

both of them are correct, also you can say I have no ticket.