Independent rights group OVD-Info said 724 people were detained across 32 different cities on Saturday.
Widespread demonstrations have broken out since President Vladimir Putin announced plans to draft 300,000 men to fight in Ukraine as part of a military “partial mobilisation” in a bid to boost the war effort.
Unsanctioned rallies are banned under Russian law – with President Putin signing a hastily approved bill that toughens the punishment for soldiers who disobey officers’ orders, desert or surrender to the enemy on Saturday.
Last week, more than 1,300 protesters were arrested during a previous wave of protests on Wednesday, and many of them immediately received call-up summons.
In Moscow, news agency AFP reported witnessing one demonstrator at the weekend protests shouting "we are not cannon fodder" as she was led away by officers, while in St Petersburg one protester told reporters: "I don't want to go to war for Putin."
Seventy-year-old Natalya Dubova told AFP that she opposed the war and confessed she was "afraid for young people" being ordered to the front.
Some of those arrested on Saturday reported being given their draft papers after being detained, a practice which The Kremlin defended earlier this week, saying "it isn't against the law".
The mobilisation ordered by Putin marked a sharp shift from his effort to cast the seven-month war as a “special military operation” that does not interfere with the lives of most Russians.
The Russian leader, and defence minister Sergei Shoigu, said the order applied to reservists who had recently served or had special skills, but almost every man is considered a reservist until age 65 and Putin’s decree kept the door open for a broader call-up.
Across Russia’s 11 time zones, men hugged their weeping family members before being rounded up for service amid fears that a wider call-up might follow. Some media reports claimed Russian authorities planned to mobilise more than one million recruits, which the Kremlin denied.
Many Russian men bought up scarce and exorbitantly priced airline tickets out of the country as as rumours swirled about a pending border closure. Thousands others fled by car, creating lines of traffic hours or even days long at some borders. The massive exodus underlined the unpopularity of the war and fuelled public outrage.
Russian forces launched new strikes on Ukrainian cities over the weekend as Kremlin-orchestrated votes took place in four occupied regions to create a pretext for their annexation by Moscow.
Ukrainian president, Volodymyr Zelensky, urged Ukrainians in occupied regions to undermine the referenda and to share information about the people conducting “this farce.” He also called on Russian recruits to sabotage and desert the military if they are called up under the partial troop mobilisation saying: “If you get into the Russian army, sabotage any activity of the enemy, hinder any Russian operations, provide us with any important information about the occupiers – their bases, headquarters, warehouses with ammunition.”