Hi, Your question is not easy to answer as there are a number of factors which may determine number of pups delivered in rats.  Strain and age of female rat are most important.  However,  I have observed rats delivering 5 to 12 pups in albino rats.  Generally older females deliver more pups than younger females. 

I agree with Arun Kumar Jaiswal.

Generally, It also depend on the number of delivery. It is known that maximum no. of pups per female is not more than 50 approx. So, for the first delivery may be 5-7 pups. Second and third may deliver more even upto 13 if female is healthy.

Ok, What about only two pups? is that an indication that there is a problem? and what should I do? thanks!

Dear Abdullah, 

I would not worry about two pups. In case I need big litter sizes I would breed the dams for that trait. From this paper you see that the dam's age affects the litter size:

Biol Reprod. 1986 Mar;34(2):322-6.

Age at puberty and first litter size in early and late paired rats.

Evans AM.

Abstract

The rate of sexual maturation among female Sprague-Dawley rats was measured in a variety of intraspecific social environments. It was found that females of this strain differ from at least one other strain of laboratory rat in that neither age at vaginal perforation nor age at first estrus was affected in Sprague-Dawley females by the presence or absence of male, regardless of his age or breeding history. Sizes of first litter among females who mated at their first estrus were compared with those among females who were first inseminated at older ages. On average, females bred at first estrus produced litters that contained more than 3 fewer pups than females mated at older ages. This observation suggests that female Sprague-Dawley rats do not attain full reproductive competence until sometime after the onset of puberty.

I have been working with mice for years. We let them mate at the age of 100 days. We did not do anything after the delivery till the pups reached puberty and had to be separated. The animal were fed pellets of good quality and water ad lib.