The North has angrily denied involvement and accused Malaysia for colluding with South Korea to frame it, while only referring to the victim by a pseudonym, without clarifying his relationship with Kim Jong-un.
The leaflets - to be flown across the border by giant, gas-filled balloons - contain details of the murder and pictures including one of a dying Kim Jong-nam slumped in a chair at a clinic in the airport.
The text describes the North's leader as "a devil who killed his own brother".
"We will start launching the leaflets in mid-March," said activist leader Park Sang-Hak, a defector who leads the Fighters For Free North Korea group.
The move was intended "to let our North Korean compatriots know the act of extreme brutality committed by Kim Jong-un", he added in a statement.
The leaflets also contain assertions by Seoul's spy agency that Kim Jong-un had executed many Pyongyang officials and ordered the half-brother's murder to strengthen his grip on power.
The text claimed that Jong-un - son of Kim Jong-Il's third wife - had ordered the assassination of Jong-nam because some viewed him as having a better claim to inheriting the leadership as their father's first-born son.
Conservative South Korean activists, including many North Korean defectors, have sent leaflets northwards for years, infuriating Pyongyang, which has at times threatened military strikes in response.