Carrying banners that featured Republic of Turkey founder Kemal Ataturk, the protesters also opposed the alleged Islamic agenda of current Turkish Prime Minister Recep Tayyip Erdogan, the BBC reported.
With the nation's presidential election set to occur next week, the demonstrators on Saturday urged Erdogan not to run.
"I feel a little scared about the developments. I would not like to have an Islamic regime in Turkey," a protestor identified as Nursel said.
"I would like to protect the secular system," she added. "That's why I am here. Especially as a female, this is very important for me."
While Erdogan has maintained he does not have an Islamic agenda, the BBC said many of Saturday's demonstrators remain convinced he would bring his religious background into play if elected president.