Can i switch sim between a iphone 5s and a iphone 4s?

I KNOW THAT THE IPHONE 5S HAS A NANO SIM BUT A I HAVE NOOSY SIM ADAPTERS I WAS JUST WONDERING IF I COULD SWITCH BACK AND FORTH.

As long as the SIM fits yea.

If your sim is perfectly fits on your phone means, you will do it.
At that same time, check whether it's your iphone 4s is unlocked or not.
If it's locked to other than your current carrier, you will need to unlock it. For unlocking you can approach your service provider or else try to buy an unlocking service from any one of the online unlocking service provider like http://www.simpleunlocking.com/apple-iphone-4s/rs16wp9/ I hope it will be very useful to you.