Assuming you are talking about cooked pork sausage, it is safe to eat for 3-4 days in the fridge. This assumes that it has been properly stored in a covered container or wrapped tightly. If you're not sure if it's still good, give it a sniff - if it smells off, don't eat it.
Cooked sausage can also be frozen for 2-3 months. Again, make sure it is properly wrapped or stored in a freezer-safe container. Thaw in the fridge before eating.