How old can you take a puppy away from it's litter if the mother passed away after the birth?

If the mother has passed away, you probably can take it from the litter a day after the mom passes away, but be aware caring for a newborn puppy without the mother is very VERY hard work that shouldn't be taken lightly. The puppy may die without the proper care or special needs such as special milk formula and needing to be fed very often with many sleepless nights. I wouldn't recommend getting a puppy like that unless you are trained to care for it and know what you're doing. NOT FOR FIRST TIME DOG OWNERS!!!!

It is better to keep the litter together until weaned if possible.