Efron, 20, has starred in three "HSM" movies -- two for television and a third to be released later this month in theaters.
The Daily Telegraph said thousands of fans showed up to catch a glimpse of him at the London premiere of "High School Musical 3: Senior Year," which he attended with his co-star and girlfriend Vanessa Hudgens.
"This will be the last one," Efron told The Daily Telegraph at the premiere. "We're all in our senior year and have graduated. It is sad but we all have to grow up some time and now it is our time. We have saved the best for last -- but this is definitely our last stop on the school trip."
New characters reportedly are introduced in the the third "HSM" and could continue the franchise should more sequels be ordered.
Efron, who also co-starred in the movie musical "Hairspray," has said he plans to headline a remake of the 1980s dance movie "Footloose."