Police said an estimated 1.2 m unregistered firearms were in circulation in the country, and anyone caught with one would be fined $325.
Officials said they identitifed between 90 and 132 private armies operating across the country which they hoped to stamp out.
However, Ramon Casiple, from the institue for political and electoral reform in the capital of Manila, told Al Jazeera that there is not enough political will to enforce the ban.
"The politicians themsleves are the ones who are organising these armed groups, he said.
"Do they have the will to the dismantle the private armies of their own allies?"
The ban is meant to reduce political violence ahead of elections, less than two months after the deaths of 57 people in the southern province of Magindanao in an election-related massacre.
Andal Ampatuan Junior, the main suspect in November's massacre, part of a politically influential clan, pleaded not guilty to murder on Tuesday.
The victims, members of another important political family, had been on their way to register a candidate for local elections when they were ambushed and killed.
More than 120 people were killed during the course of legislative and local elections in 2007, when there was a similar ban on firearms.
Almost 200 died in 2004's presidential, legislative and local elections.