Numbering around 4,000 according to the authorities, protesters held up banners and signs condemning a "genocide" in Gaza and lauding the "resistance" of the Palestinian people.
Palestinians have been "crammed" in southern Gaza and "now they are displaced again from one place to another while there are no more safe places", said 57-year-old Jaldia Abubakra, referring to Israeli evacuation orders in the city of Rafah.
Around 30 organisations called for the rally before the 76th anniversary of what Palestinians call the "Nakba" ("catastrophe"), when 760,000 people fled their homes during the 1948 war that accompanied Israel's creation.
Spanish students have set up peaceful sit-ins and camps at universities in Madrid, Barcelona and Valencia in recent days, mirroring similar pro-Palestinian campus movements across the United States and Europe.
Earlier this week, Spanish universities expressed willingness to suspend ties with any Israeli educational institution that failed to express "a clear commitment to peace".
Spain is one of Israel's harshest critics in Europe and leading efforts to recognise a Palestinian state.
The Gaza war started with Hamas's unprecedented October 7 attack on Israel, which resulted in the deaths of more than 1,170 people, mostly civilians, according to an AFP tally of Israeli official figures.
Militants also seized hostages, of whom Israel estimates 128 remain in Gaza, at least 36 of whom the military says are dead.
Israel's retaliatory offensive has killed at least 34,971 people in Gaza, mostly women and children, according to the Hamas-run territory's health ministry.
