A study of 79 firms, employing almost a million workers, found that only around 2% of fathers are taking up their right to share leave with a partner, although the figure is expected to rise.
The Working Families charity said two thirds of employers were planning to review the policy this year.
Chief executive, Sarah Jackson, said: "We're further than we should be from equality between men and women at work but this could be the beginnings of the culture change we need to empower and enable families to share care.
"These results show that employers are committed to playing their part to make shared parental leave a real option for new families.
"The scheme would help even more families if fathers could take this leave from their first day in a new job, just like mothers can.
"Employers told us that some new mothers aren't sure about giving up some of their maternity leave, which is why we need a proper period of paid time off, especially for fathers."
A Business Department spokesperson added: "Maternity leave is a day one right to help mothers prepare for and recover from childbirth.
"Shared parental leave is provided to help mothers who want to return to work early to share responsibility for the care of her child with the father or partner.
"When the policy was introduced, the department estimated that around 285,000 couples would be eligible and that the take up would be between 2% and 8%.
"Take up is likely to be higher in organisations that offer pay above the statutory minimum."