In a statement, Hamas hailed "Hani Shalouf from Rafah (in southern Gaza), who died during his work in a resistance tunnel," using its term for tunnels used for military purposes.
It did not give details of the cause of his death.
On Friday, Hamas announced that two members of its armed wing had died in separate tunnel collapses.
Hamas has run Gaza for a decade and fought three wars with Israel, which maintains a crippling blockade of the territory.
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During the last round of conflict in 2014 attack tunnels were one of Hamas's most effective weapons.
Other tunnels are used for smuggling from Egypt, although many have been destroyed by the Egyptian authorities in recent years.
At least 27 Gazans have died in tunnel incidents in recent months.