Figures show many of the 700,000 people in 300,000 rented houses and apartments have no contents insurance cover.
Landlords are supposed to insure the property in the event of it being damaged, but contents insurance for the renter's possessions is the responsibility of tenants.
The research comes as rent costs have hit an all-time high.
Jonathan Hehir, of InsureMyHouse.ie, said half of those renting had no contents cover, according to a survey his firm conducted.
He said: "With a high proportion of tenants now classified as long-term, many have acquired substantially more possessions along the way, and could stand to lose an average of €25,000 or more in the event of a fire, flood or other major incident."
Meanwhile, separate research indicates that while most people would hide if an intruder broke into their home, a small percentage would be willing to tackle the burglar.
One in 12 people said they would be prepared to take on a thief breaking into their home and would attempt to restrain them until the gardaí arrive, according to an AA Home Insurance survey.
However, four out of 10 householders would hide, and make contact with gardaí in the event of a burglary.
Men are more willing to tackle a burglar directly, compared with a tiny percentage of women.
Younger homeowners were slightly more likely than their older counterparts to say they would tackle the intruder in the event of a burglary.
Conor Faughnan, of AA Ireland, warned: "When it comes to protecting your home and family, the urge to confront an intruder is a very understandable human response.
"People get justifiably angry and scared. But it's a bad idea."
He said householders do not know the mental state of an intruder, who might even be armed.
Garda advice was that you should secure yourself as best you could and call for help, he said.
Meanwhile, an insurance product for landlords to cover them against rental income default has been launched.
The move is set to appeal to some of the estimated 300,000 landlords in this country.
Irish insurance brokerage InsurePlus has launched RentAssured.ie, a specialist product for landlords to cover them against rent default.
It is offering to cover against default of up to 11 months' rent, or €48,000, whichever is the lower figure, with average premiums of around 2pc of rental income.