The Sayer Street clinic offers sexual and reproductive healthcare, including abortions.
Demonstrator Jo Cicchini said she and about 10 others formed a peaceful 40 Days For Life prayer vigil for women and their families, and to offer them support.
Two men in the group wore grey cassocks with rosary beads tied around their waists.
A small group of women also offered support as a counterpoint to the right to life demonstrators.
Forty Days of Love spokeswoman Sarah Nielsen-Harvey said there needed to be a buffer zone similar to those introduced in Victoria and ACT last year that prevents demonstrators from coming within 150m of an abortion clinic.
She said women should not be made to feel ashamed of their choices and everyone had a right to privacy.
They also carried signs with slogans including ‘get your rosaries off our ovaries’.
“We will also be here for 40 days because we believe those grey cassocks are intimidating,” Ms Nielsen-Harvey said.
“It is the lack of laws around the clinic to prevent protesters which appear to have encouraged this group to target Perth.”
Earlier, Ms Cicchini told ABC radio the vigil “happens once a year and we are just praying for the conversion of hearts and spirits that people might change their mind about having an abortion.”
She also said the group would not harass or shame women entering the clinic.
Last February, the State Government provided $1.2 million funding for Marie Stopes International to run the private clinic in Midland to perform clinical procedures.
It came after St John of God Midland Public Hospital refused to offer pregnancy terminations or contraception on religious grounds.