The polytechnic is the first in New Zealand to gain the certification, which recognises the way it caters for and welcomes LGBT staff.
Otago Polytechnic organisational researcher Stuart Terry said the certification was a way of showing that everyone was welcome.
``This certificate tells us what we already know - Otago Polytechnic is a wonderfully inclusive place to work and has been for years.
``The Rainbow Tick is about showing we are welcoming, regardless of your background or culture.
``We are leading the way in the south,'' Mr Terry said.
To mark the certification the polytechnic was lighting its Forth St facing building up with rainbow lights every night this week and flying the rainbow flag from its Forth St flag pole and inside The Hub.
To gain certification the polytechnic showed, against a number of criteria, that it is diverse, open and inclusive as an employer.
That included having strategies and policies that specifically mentioned inclusion, reporting on inclusion at all levels and offering training to staff.
It was hoped the certification would help attract quality staff.