Monday's plea follows weeks of what the aid organisation described as the most intense destruction in Gaza carried out by Israeli occupation soldiers since the start of the Intifada in September 2000.
Almost 800 families are in need of urgent cash assistance to get back on their feet after Israel's most recent onslaught in the camp.
"In the hardest-hit place in the Gaza Strip there are few places to turn for assistance. Rafah was always a poor place. It is now a devastated place," said UNRWA Commissioner General Peter Hansen.
Earlier this month, at least 1650 Rafah residents were made homeless in the wake of an Israeli troop rampage that lasted 72 hours.
Fifty-five Palestinians, mainly civilians, were killed. Almost $11.5 million is needed just for housing reconstruction in Rafah after Israel bulldozed dozens of civilian homes during the invasion.
Cash is also needed to provide food, household equipment, medical supplies and the reconstruction of sewage and water networks.
Urgent world plea
"Hundreds of destitute families are relying on UNRWA and the international community to come forward and help them cope with a very grave humanitarian crisis," said Hansen in a statement.
A total of 21,142 people have been made homeless since 30 May this year because of Israeli invasions, added UNRWA. The organisation has been able to build shelters for less than one third of them.
Nearly $38.5 million is needed for housing in Gaza.
Following the raid, Hansen toured the damage in Rafah and warned that the camp faced an "extremely serious humanitarian situation that is much worse than other [situations] that had been characterised as disasters."