It is common practice for guests at weddings to give cash, placed in envelopes, rather than gifts.
Hoang Thi Khanh Linh, 20, is accused of stealing more than 200 million (US$8,140) from weddings.
She told the police she came up with the plan after noticing that families are usually busy receiving guests and do not pay much attention to the gift money.
She was caught red-handed last Wednesday at a house in Dan Phuong District, where she pretended to be a guest at the wedding.
She went up to the second floor, entered a bedroom, opened a cupboard, and stole a bunch of envelopes with cash when the house owner walked in.
The police found she had taken 51 envelopes containing VND19.7 million.
She told them she had committed four similar thefts in Hanoi's Dan Phuong and Phuc Tho Districts.