According to Genesis, one pair of each kind of unclean animal entered Noah’s Ark. Genesis 7:2 distinguishes the unclean animals from the clean animals brought in greater numbers.
The passage says Noah should take seven pairs of every kind of clean animal, while taking one male and one female of every kind of unclean animal. Genesis 7:8–9 then summarizes animals entering the Ark in pairs, male and female.
This is the source of a common counting issue. Some readers remember only the phrase “two by two,” while others remember the larger number associated with clean animals. Both details occur in Genesis, but they apply to different categories. The question asks specifically about unclean animals, for which the stated number is one pair.