State media reported that they arrived along with a state-of-the-art air defence system.
They are expected to install the system and teach Niger's army how to use it.
The West African country is one several in the Sahel region ruled by military authorities to have recently strengthened ties with Russia.
A spokesperson for Niger's military government on Friday said the Russians were in the country to train soldiers.
The Russian Defence Ministry's paramilitary group Africa Corps, also known as the Russian Expeditionary Corps (REK), wrote on Telegram that this was the first group of servicemen and volunteers to go to Niger.
In an attached video, a serviceman of the corps said in French that they were there to "develop military cooperation" between the countries and had brought "various special military equipment" to help with training.
Footage of the Russian instructors unloading a cargo plane full of equipment was broadcast on Niger's state television.
Ulf Laessing, a specialist in the Sahel region for the Konrad Adenauer Foundation, which promotes democracy, told the BBC World Service's Newsday programme that the military supplies appeared to be part of a "regime survival package"
Niger's democratically elected President Mohamed Bazoum was overthrown last year by the junta, which has since cut military and diplomatic ties with France - the former colonial power - and revoked an agreement with the US.
The European Union suspended its security cooperation with the country in the wake of the coup.
Mr Laessing said the military government was still concerned about some form of physical interference in Niger by the political and economic alliance of West African states, known as Ecowas.
He added that this is probably the reason for the supply of a Russian air defence system, rather than to help suppress Islamist fighters.
"I don't have any other explanations because jihadists don't have planes," Mr Laessing said.
