Abstract: The Key fiber morphological features including the fiber length, fiber width, cell wall thickness, ratio of length to width, and ratio of cell wall thickness to lumen diameter of reaction wood in secondary Bethla alnoides natural forest stands were determined and analyzed. The results showed that the fiber length of the tension wood was longer than that of the oppression wood, while the fiber width, cell wall thickness and the ratio of cell wall thickness to lumen diameter of the tension wood was smaller than those of the oppression wood. There were great differences in the fiber morphology between the two categories of wood. The fiber length in the two areas of reaction wood was longer, whose ratio of length to width was larger than 35 while the ratio of cell wall thickness to lumen diameter was smaller than 1, indicating all of these categories of wood were superior for papermaking.