The supermarket giant was rated joint 62nd of 67 businesses in an 'ethical bonus index' from donor information website Intelligent Giving.
The index ranks corporates according to how well they promote internal giving through schemes such as payroll giving and offering paid time off for staff to volunteer.
It found that Tesco - one of the sector's most generous benefactors in terms of giving money - did little to encourage staff to develop regular giving or volunteering habits.
"Its fixation on one-off donations to its own charity looks more like great PR than a serious incentive for staff to help charities," said Neill Ghosh, a researcher at Intelligent Giving.
Tesco gave more than £40m to charities in 2005/06, according to the site.
But it paid no top-ups on regular donations made by its 250,000 UK staff, did not cover the administration costs of its payroll giving scheme and offered a 100 per cent top-up on staff fundraising events only for its own charity of the year.
Events fundraising for other charities is awarded only a 20 per cent top-up.
A spokeswoman for Tesco said the Tesco Charity Trust donated more than £700,000 in the past year to charities chosen by staff for their own fundraising events.
She added that the company gave more than 1 per cent of pre-tax profits to charities in the form of donations, staff time and gifts in kind.
Financial services company Aviva, which owns Norwich Union, is at the top end of the index.