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.

The original school building was built in 1969 and in 1992 a new wing was added in order to accommodate both the increase in student population and the change in school program. A second addition of 10 classrooms opened in the spring of 2002. The school has two gyms, one larger than the other. The school also has three music rooms, one for vocals, one for strings, and another for band.

In 2003, the Town of Richmond Hill contributed 10 "Character Matters" signs to the school as part of an initiative that encourages young adults to become more involved in their community. This event featured guest speaker Wendel Clark, the former Toronto Maple Leafs Captain.

• Ramin Karimloo: stage actor
• Mobolade Ajomale: Olympic sprinter
• Hannah Alper: activist, blogger, and motivational speaker
• Scott McGillivray: entrepreneur, investor, television host, author, and educator
• Evan Taylor Benyacar: actor, stunt artist

• Education in Ontario
• Sir Alexander Mackenzie Senior Public School, another similarly named school in the Greater Toronto Area, but after a different person named Alexander Mackenzie
• List of secondary schools in Ontario

• Official site