The U.N. noted that the North's bureau director for its foreign ministry, Ja Song-nam, attended a signing event at U.N. headquarters on Tuesday.
The optional protocol is an international treaty that contains 17 clauses related to child trafficking, prostitution and pornography.
The treaty also contains specific regulations, punishment measures and global cooperation guidelines regarding victimized children.
In 1989, the U.N. adopted the UNCRC in a bid to allow children to grow up in a healthy and safe environment, which North Korea ratified in 1990.
An additional optional protocol was brought up in 2000 supplementing the former treaty, which 121 countries signed and 168 have since ratified.
The reclusive country's signing was initiated in May during a Universal Periodic Review at a U.N. Human Rights Council meeting in Geneva, Switzerland. The council advised the North to consider ratifying the protocol.
Accepting the convention, North Korea is to submit in two years a report regarding the steps it has taken to carry out the protocol. The U.N.'s Committee of the Rights of the Child will examine it before putting the convention into effect.
The North's authorizing the protocol for children's rights along with the convention for the Rights of the Disabled in July are prompting speculation that the cloistered country is seeking to ward off international criticism about its alleged human rights violations.