The present invention relates to a composite including chitosan and/or chitin and a catechol-based compound, an organic reinforcing material composition including the composite, a product manufactured by using the organic reinforcing material composition, and a method for preparing a chitosan and/or chitin composite with improved strength, including the step of adding the catechol-based compound to chitosan and/or chitin. The chitosan and/or chitin composite including the catechol-based compound is advantageous in that it is able to maintain high strength in a wet-swollen state by improving the problem of strength reduction due to moisture, compared to the composites containing no catechol-based compound.
