There is provided a spout assembly that is prevented from breaking due to ultrasonic vibration during welding and is readily separated from a packaging container when being broken down, and a packaging container with the spout assembly. A spout assembly includes a spout and a cap. The spout has a cylindrical sidewall; a cylindrical base provided at the lower end of the sidewall and having a larger outer diameter than the sidewall; and a disk-like flange extending outward from the lower end of the base. The cap has a cylindrical peripheral wall with an internal thread and is screwed from the upper end side of the spout sidewall. The spout sidewall has an external thread engaging the internal thread of the cap and a recess located between the external thread and the base.