STORY: Demonstrators in Lima threw objects at police, who responded by firing tear gas.
Protesters demanded the resignation of current President Dina Boluarte, closure of Congress, changes to the constitution and Castillo's release.
Castillo is serving 18-month pretrial detention while he is investigated for "rebellion," a charge the former president denies. He was ousted after he tried to illegally dissolve Congress and reorganize the judiciary.
Boluarte, a former vice president who assumed power shortly after Castillo's removal, has proposed bringing forward the next general elections.
Almost two dozen died in protests across the country last month.