"We decided not to join. We weighed all the pros and cons and decided it is not obligatory for us," Mikhail Ulyanov, who heads the foreign ministry's non-proliferation and arms control department, told TASS state news agency.
He criticised the "too weak treaty" which however "places certain burdens on its participants".
"We don't have a negative attitude to this treaty but we don't see the point of joining it," said Ulyanov, arguing that Western countries and Russia already have export controls in place, and that the treaty would not be effective for developing countries.
China, also a permanent member of the UN Security Council, has not signed the treaty either.
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UN Secretary-General Ban Ki-moon this month urged all member states to sign up.
The first major arms accord since the 1996 Comprehensive Nuclear Test Ban Treaty, the ATT covers international transfers of everything from tanks to combat aircraft to missiles, as well as small arms.
The treaty compels countries to set up national controls on arms exports. States must assess whether an exported weapon could circumvent an international embargo, be used for genocide and war crimes, or be used by terrorists and organised crime.