His hosts were expected to press him to ease restrictions on Palestinians in the West Bank and Gaza.
At Israel's airport before leaving, Olmert said he expected productive talks with Turkish leaders, including Prime Minister Recep Tayyip Erdogan and Foreign Minister Abdullah Gul.
"We have good relations, we speak frequently and I'm looking forward to talking with them, Olmert told reporters. Olmert is also scheduled to meet Turkish President Ahmet Necdet Sezer on Thursday before returning home.
Turkey's Islamic government has good relations with both Syria and Hamas, the militant Islamic group that heads the Palestinian government, and also with Iran, with which it shares a long border.
Israel considers Iran a strategic threat, suspecting that Iran is building nuclear weapons, despite its denials. Iran's president has repeatedly called for Israel to be wiped off the map. Olmert hopes to enlist Turkey in accelerated efforts to keep Iran from going nuclear.
Turkey will likely press Olmert to work with a new Palestinian government
after last week's agreement by Hamas to join a national unity government with the more moderate Fatah of President Mahmoud Abbas. Israel and the West have reserved judgment, insisting that any Palestinian government must recognize Israel, renounce violence and accept previous peace deals.
Israel, the United States and Europe ban contact with Hamas, which they label a terror group.
Turkey is also expected to urge Israel to accept peace overtures from Syria, but Israeli officials say Syria is interested in peace talks, not peace - as a way of ending its diplomatic isolation.
Before leaving Israel, Olmert acknowledged Turkey's potential, saying it is an important country economically, diplomatically.
In Turkey, about 50 demonstrators protested the visit hours before Olmert's arrival. "Murderer Olmert! Get Out!" read a banner carried by the group in downtown Istanbul.
PMO mum on issue of executed spy's remains
The Prime Minister's Office on Wednesday refused to elaborate on reports that Olmert was to ask Turkey to assist in retrieving the remains of executed Israeli spy Eli Cohen from Syria.
Cohen's 71-year-old widow, Nadia, said on Tuesday that Olmert had promised her he would raise the issue during his meetings in Turkey.
Egyptian-born spy Eli Cohen infiltrated the Syrian government before he was discovered and hanged in 1965.
Israel has appealed in the past to Syria via European intermediaries for Cohen's body without success.