Can you put guinea pigs in the same cage as hamsters?

NO guinea pigs should not be housed with any other animals except for their own kind. It would most likely end in one (most likely the guinea pig since they are more docile) being seriously injured or killed.

Goddesskieryn: The two animals have seriously different habitat and food needs. While the guinea pig needs extra vitamin C in its diet, that much sugar would be bad for the rats. Not to mention that guinea pigs have rather bad eye sight, and rats being very good climbers need many levels in their cages. Guinea pigs living with multiple levels and bad eyesight equals a falling piggy. If they fall from say a third level they could be seriously injured. Also guinea pigs need long open spaces to run and play, i believe the rule of thumb is something like 7.5ft of space for up to 2 pigs.