A safety intravenous cannula and catheter device is disclosed. The device permits easy insertion of a cannula made of a biocompatible material into the vein with a guide needle and withdrawal of the guide needle into a safety chamber with an in- built locking mechanism with completely prevents removal and/reuse of the needle. The needle before insertion is protected by a biocompatible sheath which when inserted into the vein and after withdrawal of the needle acts as catheter. Similarly, after withdrawal the needle is locked inside a safety chamber in such a manner that at no time does the user come into contact with the needle or in any danger of accidental injury.