Abdullah's visit to Ankara is the last stop of a four-nation European tour, which included Britain, Italy and Germany. It is the king's second visit to Turkey in less than two years in a sign of Ankara's growing ties with the oil-rich kingdom.
Turkey has massed tens of thousands of its troops in the southeast of the country following a series of attacks by Iraq-based rebels of the Kurdistan Workers' Party, or PKK, that has left nearly 50 dead since September.
Turkey is facing international pressure to avoid a wide-scale cross border attack on PKK bases in northern Iraq, out of fear such an operation would destabilize what has been the calmest region in the country.
The Saudi king's visit is also taking place as Turkey is playing an increasing role in bringing together the sides in the Middle East conflict. Next week, Israeli President Simon Peres and Palestinian President Mahmoud Abbas will both address Turkey's parliament.
Turkey is Israel's closest ally in the Islamic world and has been forging close ties with the Arab world over the past few years.
Last week, Foreign Minister Ali Babacan visited Arab nations, including Saudi Arabia, for talks on the Middle East peace efforts and to explain his country's military planning for an incursion into northern Iraq.
Arab governments have been trying to strike a balance amid the mounting crisis between Iraq and Turkey, seeking to avoid openly criticizing Ankara and urged dialogue between the two sides, a reflection of Arab countries' fears of a widening of the Iraq conflict.
The king was schedueld to meet Gul at the presidential palace, where he will be received in a ceremony with military honors and also hold talks with Prime Minister Recep Tayyip Erdogan. The king will be decorated with Turkey's highest state medal during his stay.
Abdullah last came to Turkey in August 2006. It was the first visit by a Saudi monarch in 40 years. Trade ties between the two countries have increased by threefold over the past five years, to reach US$3.3 billion, a statement from Gul's office said.
In Italy, Abdullah was received at the Vatican by Pope Benedict XVI in the first-ever meeting between a pontiff and reigning Saudi king, the protector of Islam's holiest sites. In Britain, the king discussed terrorism and the Middle East peace process with Prime Minister Gordon Brown.
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969