Soymeal, which contains natural plasticizer and tackifier, has been used to fabricate biodegradable and low-cost warp sizes, with potential for replacing non-biodegradable polyvinyl alcohol (PVA) sizes for large-quantity industrial applications. Warp sizes from soyprotein isolates (SPI) have been reported as a potential substitute for PVA sizes, which contribute to high chemical oxygen demand in textile effluents and cause serious water pollution. However, sizes from SPI are high in cost and need additional plasticizers to overcome brittleness of films. In this research, the developed low-cost soymeal sizes contain soyprotein as majority and saccharides/saponified-oil from soymeal as minorities. Comparing to films from triethanolamine-plasticized SPI sizes, the soymeal size had about 30.1, 25.2 and 8.3% higher film flexibility, adhesion to yarns and abrasion resistance, respectively. Saccharides in soymeal and saponified oil formed during size extraction functioned as plant-based additives with capability of improving adhesion of protein sizing pastes to cotton and/or polyester yarns and increasing elongation of protein-based size films. Successful utilization of soymeal in textile sizing will lead to its large-quantity application, resulting in high value addition to agricultural byproducts and profound impact on soybean industry and textile industry. (C) 2016 Elsevier B.V. All rights reserved.