Lightweight structural materials with high strength and toughness are highly desirable for many advanced applications. Wood, as a sustainable structural material, is widely used in engineering due to its abundance and excellent mechanical properties. In this paper, we report a self-densification strategy to develop super-strong wood by reassembling highly aligned wood fibers as functional units and self-densified without the need for hot pressing. The resulting self-densified wood exhibits ultra-high tensile strength (496.1 MPa), flexural strength (392.7 MPa) and impact toughness (75.2 kJ/m²), surpassing those of compressed densified wood and traditional metal materials like aluminum alloys. Notably, the self-densified wood exhibits uniform shrinkage in the cross-section while maintaining its longitudinal dimension. This characteristic leads to an order-of-magnitude enhancement in the overall mechanical performance of the wood, presenting a significant advantage over compressed densified wood. Such super-strong yet lightweight wood has great potential for application as a sustainable engineering material, replacing traditional structural materials such as metals and alloys.