A new survey from the Central Statistics Office shows that the average income of those aged over 65 decreased by 5% between 2009 and 2011.
CSO figures also show that the proportion of over 65s living in consistent poverty almost doubled over the same period rising from 1.1% to 1.9%.
Between 2009 and 2011, those aged over 65 saw their average weekly incomes fall from €429 to €407.
The CSO said this reversed the upward trend in the income of the elderly which increased by 48% between 2004 and 2009.
Although the proportion of the at-risk of poverty rate rose only marginally over the two-year period, the share of the pensioner population experiencing two or more forms of enforced deprivation rose from 9.5% to 11.3%.
The measure identifies the proportion of below-average earners who are deprived of two or more goods or services that are considered essential for a basic standard of living.
In 2011 nearly 55% of the elderly population were women, while just over one third of the elderly were widowed, divorced or separated.
52% were retired and just over 7% were at work.
More than 87% were living in owner-occupied accommodation, while more than 56% said that they suffered from a chronic illness or a health problem.