In a rare protest in the Gulf state, men wearing traditional long white tunics and women dressed in black raised banners and shouted slogans critical of Israel.
Palestinians also joined Monday's demonstration, which was organised by Doha's city council.
"Palestinians are an Arab and Muslim people to whom we are related through blood, language and religion ... If the Qatari people ignore the suffering of the Palestinians, it would be like ignoring themselves," said Fahd al-Sweillem, the council's secretary general.
Thousands of Yemenis also took to the streets of the capital Sanaa on Monday to demonstrate solidarity with Palestinians and urged the United Nations end the Israeli operation.
Protesters backed by Yemeni political parties including the ruling General People's Congress burned an Israeli flag as they chanted "Allahu akhbar" (God is great).
Syria, Lebanon and Egypt have also witnessed protests in the last week since Israel began its action following the kidnapping by Palestinian fighters of an Israeli soldier on June 25.