To improve pleat-processing effect of natural fiber materials easily and surely by an industrially advantageous method without generating environmental problems, improve the wearing comfort of the pleat-processed products, develop the usages of a wide range, and provide a pleat-processed products excellent in touch feeling and durability along with the above improvements.

This new method for pleat-processing is provided by imparting a high concentration urea together with an acid bonding agent on the fiber material in using a hydrophilic dichlorotriazine-based compound singly or as a mixture as a cross-linking agent, and heat-treating. The processing method achieves the pleat-processing, excellent in touch feeling and durability for the natural fiber materials by a method of without generating the environmental problems, improves the wearing comfort of the pleat-processed products and also aims at the development of the usages of the wider range.