Use of prolactin as hepatoprotector and/or hepatic cell regenerator in mammals. The present invention relates to the use of prolactin (prl) to preserve the function of liver cells as well as to promote the regeneration thereof in mammals. The hepatoprotective function is due to the induction of transcription factors such as c/ebp α, hnf-1, -3, -4, vegf and hif-1 α and the regenerative function, to the increase of the activity of the transcription factors ap-1 and stat-3. The induction of all these factors involved is due to the action of prolactin administered in a single dose that avoids the side effects that occur with higher doses or with the administration of other drugs that have the same use.