Inorganic calcium sulfate whisker (CSW) was surface modified with sodium hexametaphosphate (SHP) as waterproof modifier to reduce the solubility, and subsequently CSW/SHP was further modified using the coating of silica to improve water tolerant and enhance the bondability between CSW and wood fibers. Through the dual-surface modification, electrical conductivity (EC) of the pure unmodified CSW decreased dramatically and reached an equilibrium value of 73.9 mu s.cm(-1) in the CSW/SHP/SiO2 solution. The mechanical properties of hybrid handsheets containing 2.5-20 wt.% modified fillers were investigated, and the retention of the modified fillers was higher than that of unmodified fillers. (C) 2014 Elsevier B.V. All rights reserved.