Leslie Black, 29, entered the plea Tuesday in a Prince Albert courtroom.
A judge ordered the man to undergo a psychiatric assessment and he was remanded in custody until June 26.
Marlene Bird was found badly injured in a parking lot outside a community centre in the city's downtown on June 1, 2014.
The 57-year-old was so badly burned in the attack that doctors were forced to amputate both her legs. She also had several surgeries for skin grafts.
There was an outpouring of support for Bird nationally and internationally and a local shelter set up a trust fund to help cover medical expenses and rehabilitation costs.
Bird later moved into a home with her long-time partner, who helped her adjust to her new life in a wheelchair.
Police initially charged Black with aggravated sexual assault. A publication ban on Bird's name was lifted after her family argued that she didn't want to be "just another statistic."
The Crown told court that charge will be dropped.