My baby is 5 months old. He passes stool once in 3-4 days since a month. Is that normal?

yes mom it is very much normal :) even my kids passed stool once in 3 to 5 days around this age, and the doc told me this is absolutely fine. as your baby moves towards solids, his stool routine will get more regular. in the meanwhile, keep a track of how many times he passes urine to make sure he is not dehydrated or in distress.