Spring is mating season for panda bears. The mating season runs from mid-March to mid-May. During this time, however, a female panda only has a window of three to seven days annually in which to conceive. This period of being in heat is known as the estrous cycle. Pandas generally reach reproductive maturity at the age of seven, and it lasts until they are around 20 years old (with their life expectancy estimated at about 30 years in the wild).

Pandas are solitary animals. This usually means there are few males in the vicinity of a female panda in heat. As few as two and as many as five will typically compete for the right to breed. The largest male usually emerges the victor after some roaring and aggressive pushing. The female panda will attract her mate with scent-marking (rubbing against trees and urinating) and bleating calls.

The male panda mounts the female from the rear for penetration. Sex lasts anywhere from thirty seconds to five minutes. The male panda leaves the female after copulation and will play no role in raising the offspring. Panda pregnancy lasts between four and five months, broken into two distinct phases. The first two to three months are known as "delayed implantation." The fertilized egg divides a few times and the segments float around in the uterus. After this phase, the embryo finally attaches itself to the uterine wall, beginning the second phase, the two month gestation period.

A female panda is biologically wired to reproduce every two years. However, if her cub dies before it's six months old, she may reproduce again the next year.

The mother panda digs out a den in which to give birth and raise her cub. Pandas give birth to either one or two offspring, and very rarely three. Newborn pandas require so much care from their mother that she is only capable of raising one cub. The second is left to die. It is unknown how female pandas decide which cub to raise. Panda cubs are the smallest newborn mammals, excluding marsupial babies. At about five ounces and 16 centimeters long, they are about 1/900 the size of their mother. Panda cubs are born pink with short white hair, with their eyes closed for at least a month after birth. The hair slowly grows, becoming gray before turning black.