Alexander Mackenzie High School (AMHS), formerly known as Don Head Secondary School is a public secondary school with classes for students in grades 9 through 12, located in Richmond Hill, Ontario, Canada. The school opened in 1969 as Don Head Secondary School and was renamed Alexander Mackenzie High School in 1992, in honour of Major Addison Alexander Mackenzie, a Richmond Hill resident and philanthropist.

It was announced in October 2008 that AMHS will join Huron Heights S.S., Unionville High School, and Westmount Collegiate as one of the four high schools in York Region to offer a specialized arts program. This program is known as ARTS Mackenzie and encompasses dance, theatre arts, music and visual arts.

In 2017, AMHS, along with G.W. Williams SS, Maple HS, Miliken Mills HS, joined Bayview SS as the board's IB Diploma Programme schools.