Christian Aid's Manchester headquarters has received a second anonymous donation of £4,000 in cash through the post.
Stunned staff opened a bubble-wrapped package earlier this month that contained four £1,000 bundles in £10 notes, without an accompanying letter.
The surprise donation comes 18 months after the charity received a similar donation, then in £20 notes, and again for £4,000 without explanation.
Christian Aid's area manager Kerry Starkey said both donations were a "complete mystery", but added that the charity wanted to thank whoever sent them in.
She said she was also surprised that the package had arrived at all because the address was inaccurate, and the postcode was missing.
Starkey told Third Sector: "We think it is the same person as both times the gift was made up from old bank notes without a letter."