A valve stem with an adjustable tire pressure detector has a tire pressure detector, a valve stem body, a conducting member and a fastening assembly. The tire pressure detector has a guiding slot, a concave surface and a convex surface. The guiding slot is formed through the tire pressure detector and forms two openings. The concave surface and the convex surface are formed on the tire pressure detector respectively adjacent to the openings. The valve stem body is moveably mounted through the guiding slot and has a head being moveably mounted on the concave surface. The conducting member is mounted on the concave surface or the convex surface and is electrically contacted to the valve stem body and the tire pressure detector. The fastening assembly mounts the valve stem body on a rim securely.