The opportunistic thief struck at the WRVS Russell Centre in Hyde Road on Tuesday July 29 at 3.45pm. They walked in off the street and took a red metal cash tin containing £900.
Part of the money was takings from the week but the majority was money that was being saved for Christmas. Centre development manager Mal French said she was devastated.
"Some of this money was to help provide extras at the centre, especially saving towards the Christmas festivities," said Mal.
"In view of the visitors we have here at the Russell Centre, the older person and most just on a pension, funds are limited. I am absolutely gutted."
The centre is now appealing for support from local businesses which may be able to provide gifts for a raffle for the centre to recoup some of the lost cash.
Police are investigating and anyone with any information is asked to contact 0845 60 70 999 and quote serial number EE1-6158-08.
Organisations interested in helping can contact Mal French on Eastbourne 412279.