This is what is written on the last page of Nepali passport: Notice: 1. The passport is valid for the period specified on the photo page. This means that the passport is INVALID beyond that date. You have a good case but why take unnecessary chances? If a good-hearted fellow checks your both passports, he may probably let you through. But a stubborn officer might successfully argue that your expired passport is simply irrelavant. So the onus lies on you to produce a valid document to the officers at port. My suggestion: get a new visa on the new passport. It might not be difficult as you already have one, albeit on an expired passport.