The planes arrived disassembled on October 2 at a military airport in the Belgrade suburb of Batajnica.
The MiGs are being provided by Moscow at no charge, but their assembly, repair, and refurbishing costs are expected to be near $235 million in total.
The final four jets are set to arrive sometime before October 20, when they are likely to be displayed in Belgrade during a Liberation Day parade. Russian Defense Minister Sergei Shoigu is scheduled to attend.
In March, Serbia’s Aleksandar Vucic, then prime minister and now president, confirmed earlier reports that Russia would provide the six MiG-29 fighters "as a gift."
He added that the planes would enter military service by the end of 2017 after refurbishing and pilot training.
Images of first two disassembled MiG-29 aircraft from #Russia at #Batajnica Air Base (#Belgrade, #Serbia), arrived on Monday afternoon. Fighter jets were transported by An-124 "Ruslan" cargo plane. All six are to arrive by the end of this week. pic.twitter.com/S5qhS6BUoC— Global Defence (@WoDSerbia) October 2, 2017
Russia also committed to provide 30 T-72 tanks and 30 BRDM-2 patrol combat vehicles to Serbia for free.
Vucic said on October 2 that Serbia also planned to improve its defenses and has been negotiating with Moscow for the purchase of Russian-made S-300 antiaircraft systems.
"We will continue to protect our freedom and independence," Vucic said.
Vucic, a former nationalist, has remade himself as a pro-European Union reformer while seeking to maintain good relations with traditional ally Russia, which is looking to block the Balkan nation’s path toward possible NATO membership.
Serbia’s moves to heighten military ties with Moscow have worried the West and many neighboring countries, including Bosnia-Herzegovina and NATO member Croatia.
A NATO official told the Associated Press that "the defense equipment which NATO's partners procure is a sovereign choice for those countries. There are no restrictions imposed by NATO."