| Sir John A. Macdonald Collegiate Institute | |
| Address: | 2300 Pharmacy Avenue |
| Country: | Canada |
| Coordinates: | 43.7869°N -79.3238°W |
| Motto: | Prudentia et Scientia |
| Motto Translation: | Vision and Knowledge |
| Religious Affiliation: | Secular |
| Founded: | 1964 |
| Schoolboard: | Toronto District School Board |
| Superintendent: | Ian Alison |
| Trustee: | Manna Wong |
| School Number: | 4154 / 941948 |
| Principal: | Gregory Foulidis |
| Administrator: | Patty Bowman |
| Campus Size: | 18.14 acres |
| Grades: | 9-12 |
| Enrolment: | ~900 |
| Enrolment As Of: | 2022-2023 |
| Colours: | Red, Purple, and Black |
| Mascot: | Angus Blackscot |
| Team Name: | Macdonald Blackscots |
| Feeder Schools: | J.B. Tyrrell Sr. Public School Pleasant View Jr. High School |
Sir John A. Macdonald Collegiate Institute[1] is a secondary school in Toronto, Ontario, Canada. It is located in the L'Amoreaux neighbourhood of the former suburb of Scarborough. It is operated by the Toronto District School Board and previously by the Scarborough Board of Education. The school's motto is "Prudentia et Scientia" (Vision and knowledge).
Sir John A. Macdonald Collegiate Institute was designed by the architectural firm, Gordon S. Adamson and Associates. The school building, originally named O'Sullivan Secondary School, was constructed in 1963 and opened in the fall of 1964 when there was only farmland around it, and as the population in the area grew, so did the school. During construction, O'Sullivan was renamed to Sir John A. Macdonald Collegiate Institute, after Canada's first prime minister, John A. Macdonald, in which the colours red, black, white and purple were chosen, with the latter colour taken from the $10 Canadian banknote.
As its eleventh collegiate, the school's main building was then extended to have more classrooms, along with larger rooms used for music, art, and autoshop. MacDonald celebrated its 50th year on September 26, 2014.