The two opened the fair on the second day of Hu's visit to Russia.
Nearly 200 Chinese companies are showcasing their products at the fair, said to be China's biggest ever in a foreign country.
Hu's visit is aimed at cementing growing economic and political ties between the two countries.
After talks on March 26, the two presidents pledged to further develop energy cooperation. They also reiterated their aligned positions on Iran and North Korea's nuclear programs.
In talks with Prime Minister Mikhail Fradkov earlier today, Hu proposed more frequent meetings to pave the way for increased trade.
The Chinese president is also scheduled to travel to Russia oil-rich republic of Tatarstan today.
(compiled from agency reports)
An oil field in Russia's Republic of Bashkortostan (TASS file photo)
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