Authorities at Bangkok's international airport found a tiger cub that had been drugged and hidden in a suitcase.
They made the discovery after the woman, a Thai national flying to Iran, checked in and her bag was sent for a routine X-ray because it was overweight.
The X-ray showed a live animal inside. A toy tiger had been placed beside it in the suitcase in an apparent ploy to fool any inspection.
The 31-year-old woman was arrested at Suvarnabhumi airport before boarding her Sunday flight. The cub, estimated to be about three months old, was sent to a wildlife conservation centre in Bangkok.
A DNA test is expected to provide details about its origin, said officials at the centre, explaining that this would help determine whether it was captive born or taken from the wild.
The cub could have fetched about 100,000 baht (£2,000) on the black market in Iran, where it is popular to have exotic pets.
The woman faces up to four years in prison. Conservationists want to see the penalty raised to ten years to deter animal traffickers.