According to Genesis, one pair of animals classified as unclean entered Noah’s Ark.
Genesis 7:2 distinguishes between clean and unclean animals before Noah enters the vessel. It instructs Noah to take seven pairs of every clean animal, but one pair—male and female—of animals that are not clean. Genesis 7:8–9 then summarizes animals entering in pairs.
The distinction is often overlooked because many simplified retellings say only that Noah took animals “two by two.” That phrase captures the paired entry but leaves out the more detailed instruction about clean animals.
The passage does not provide a modern zoological classification. “Clean” and “unclean” are categories within the ritual framework of the biblical text, and later Genesis describes Noah offering some clean animals in sacrifice. The number therefore depends on reading the specific instructions in Genesis 7 rather than relying on the popular summary alone.