Hello how may I help you? What is the longest thing in the world? I'm afraid that question is too vague What is the longest river in the world? The longest river is the Amazon How long is the Amazon river? It is 1200 km long How much longer is it than the 2nd longest river in the world? That is 50 miles longer than the 2nd place river Where does it start and end? It starts in Brazil and ends in Chile.