This study characterizes the fracture behavior of a shear-thickening fluid (STF) with 58 vol% dispersion of styrene/acrylate particles in ethylene glycol. Double-cantilever-beam specimens with the STF as adhesive layer were utilized to characterize the mode-I fracture energy of the fluid with fluid thickness varying from 0.2 to 2.05 mm, and crack opening displacement rates from 1 to 50 mm/s. It was found that the deformation behavior of the STF was rate sensitive. In particular, liquid-solid transition could occur by increasing the loading rate and/or decreasing the fluid thickness. As confirmed by the high-speed video recording, the STF showed a "solid" behavior, fracturing with crack growth in a brittle manner when the displacement rate was greater than 30 mm/s. Thus, the average mode-I fracture energy of the fluid could be determined. It is interesting to note that the measured G (c) of the "solidified" STF was almost constant at similar to 230 J/m(2), which is comparable to a low cross-linked epoxy. The results demonstrate that the deformation behavior of the STF in solid phase can be characterized by the standard test method following classic fracture mechanics. The measured fracture toughness can be used as an effective parameter showing the crack resistance or the energy-absorbing capacity of the STF in the solid phase.