The six were en route to study a government forestry programme in a remote mountainous area of Compostela Valley on the island of Mindanao when they were snatched Friday, the military said.
No one has claimed responsibility for the abduction, although various armed groups are known to operate in the area, including communist guerrillas and private security personnel who work for illegal loggers and miners.
"Our concern is the safe release of the civilians," regional military spokesman Lieutenant General Rainier Cruz said, as he deployed troops to help local police track down the victims, who work for the Department of Environment and Natural Resources.
The rangers are often poorly equipped and up against illegal loggers backed by a private armed unit and sometimes corrupt local officials, the department has said.