Figures from the European Consumer Centre (ECC) showed 133 people had a problem with the no-frills operator while its main rival Aer Lingus faced less than half that number.
Only 62 travellers had a problem with the soon-to-be privatised airline.
The most common disputes were over-delayed, damaged or missing luggage, and delayed or cancelled flights. But the ECC suggested only a third of people who experience difficulties when they fly are prepared to make a complaint. That figure has been backed by research from the European Commission.
The consumer body also warned about airlines failing to meet obligations toprovide for passengers facing delays or cancellations.
Under legislation travellers are entitled to a refund or re-routing otherwise the airline must provide refreshments, meals and accommodation.
Many are being asked to look after themselves and invoice the airline when they return from their journey, completely at odds with the legislation.
“That’s not the way it works. Is it a tactic to reduce the number of claims? We cannot say, but it creates a double inconvenience,” the ECC spokeswoman said.
She added that an upsurge in complaints against airlines was expected following the terror threats in Britain.
Ryanair defended their record on passenger satisfaction with only 133 complaints after carrying 6.2 million passengers in the six-month period.
Aer Lingus declined to comment.
The ECC noted, however, there were a small number of complaints from passengers who missed flights, had problems with tickets booked online or sought refunds for not making flights due to illness or injury.
It said the complaints were mostly unfounded.
Other airlines operating in and out of Ireland faced 178 complaints between January and June 2006 including Air France, 20, Iberia airlines, 14, Alitalia 10, and British Airways, six.
Research carried out on behalf of the ECC for 2005 showed nearly half of all people who travel by air experienced a problem.
A breakdown of the complaints for the first six months of the year showed 103 were about luggage and the same amount for flights pulled off the schedule.
Six people complained they were not allowed on to flights due to overbooking.