A study by charities Age UK and Carers UK found that the proportion of older women working flexibly has fallen over the past two years, while there has been a "marked increase" in the number unemployed for more than a year.
The report suggested that many older women wanted to work, but could not find a suitable job.
An analysis of the Labour Force Survey found that 36% of women worked flexibly in 2012, down from 38% in 2010.
In the same period, long-term unemployment among women aged 50 to 64 rose from 34% to 40%.
Caroline Abrahams, of Age UK, said: "We know many older women especially are finding it impossible to hold down a full time job at the same time as fulfilling their caring responsibilities.
"In the end, many have to stop employment altogether or take a poorly paid part-time job, where their skills are often wasted and their income plummets."
Helena Herklots, chief executive of Carers UK, said: "Unless carers can access flexibility at work and reliable care services at home they are at risk of being forced to give up work entirely."