"On" is correct. In the United States, the word "my" is usually unnecessary and would usually be left out. The following examples are correct: "I will be on vacation from May 30th through June 2nd." "I took this picture while I was on vacation last year." "This is an automated message. I am currently on vacation. If you need urgent help, please contact my assistant, Ruth Adams." Here are some other examples of prepositions used with certain words. "This year I'm going on a trip." "The Boy Scouts went on a hike." "Those news articles make me afraid to get on a plane." "I've only seen the Northern Lights once in my life." "In my experience, it is better to take Route 128 even though it is a few miles longer." "In the 1960s, a manned spacecraft landed on the moon."

We say "on my vacation" in the US.

Hello, 'on my vacation' is correct. Generally, we use 'on' for things that are shorter in time. on Sunday 'in' a week 'in' a month 'in' a year If you're finding this kind of thing difficult, maybe consider booking a grammar lesson and we can go through them together.