Background Biaxial tests are important for complex mechanical behaviours of materials such as rubbers, soft materials, polymers and bio-materials, and commercial biaxial testing machines are usually expensive. Objective For convenience and cost control, an equal-biaxial device for soft materials, with a load capacity up to 100 N and a maximum displacement of 50 mm, is designed and manufactured. Methods A novel rope and pulley load system is applied in the designed biaxial device, and the device ensures automatically equal stress in two directions and minimizes possible installation deviation. The biaxial strain is measured from the central zone of the cruciform samples by a set of non-contact laser extensometer. Results The device is calibrated through an array of tests for three different types of soft materials, silicon rubber, polyimide (PI) and polyethylene terephthalate (PET). The repeatability of equal-biaxial strain-stress curves of the three materials is excellent. Possible error sources of the device are examined and their respective contributions are quantified. Conclusions Such a device offers a convenient way to carry out biaxial tests for many materials such as rubbers, polymers, and biomaterials.