Navalny, 42, spent three weeks behind bars, his second spell in detention in as many months. He was released last month after serving 30 days in prison, and soon re-arrested.
“Over the 50 days I have been in jail, we have seen yet more evidence that this regime is in complete decline,” Navalny said upon his release according to the AFP news agency, hinting at recent embarrassments to Moscow’s intelligence services abroad and the launch failure of a manned Russian space rocket.
“If anyone thinks that with arrests … they can scare or stop us, that is clearly not the case,” he added.
Navalny’s original arrest came late August, when he was apprehended for organising a demonstration at the beginning of the year.
Upon his release, the Putin-critic was immediately arrested again, this time for a protest against the raising of the retirement age.
That second arrest coincided with regional elections last month, one in which the Kremlin suffered rare defeats, with voters rejecting candidates from the ruling United Russia party in at least two regions.
In the far eastern Primorsky Krai, a runoff election will be held again in two months after accusations of vote-rigging in favour of the Moscow-backed candidate led to protests.
Over the last couple of years, Navalny has been one of Putin’s most staunch opponents. In the run-up to the 2018 presidential elections, Navalny ran a campaign focusing on battling corruption.
However, Navalny was barred from running in the elections after a Russian court reinstated a past criminal conviction for embezzlement.
The conviction had been previously overturned by the European Court of Human Rights, which ruled that Russia did not give Navalny a fair trial.
The European Union said the circumstances surrounding Navalny’s removal from the race cast “serious doubt” on the election.
Putin won the contest with 76 percent of the vote, his best ever showing.
Following those results, Navalny has remained critical of Putin and has subsequently been arrested several times.
Supporters fear that the two consecutive administrative cases mean the authorities may be getting ready to open a criminal probe against Navalny.
In that case, he could face a lengthy prison term.