The National Competitiveness Council has said that the country's uppermost personal tax rate is high in comparison to the UK.
In a report on how the Republic of Ireland is prepared for Brexit, the council also said that Ireland's 33% rate of capital gains tax is particularly high relative to the UK's 28%.
The top tax rate in Ireland sees higher earners pay 51% on every additional euro they earn after allowances.
The NCC said that personal tax is high compared to Britain, adding that tax competitiveness will be crucial after Britain leaves the EU.
In its report, the council highlighted potential infrastructural bottlenecks, including broadband and skills deficits, and said that investment in capital remains low compared to other EU states.
It also said the drop in Sterling has made the Republic less competitive.
Brexit poses a serious and imminent threat to prosperity and more must be done to prepare for it, the council cautioned.
It also warned that the UK is likely to step up investment in infrastructure and to enhance its own tax offering as its departure from the EU draws closer.
And the council said other countries will also seek to enhance their competitiveness as a big shift in global trade patterns take hold.