Patient-specific tissue-mimicking phantoms have a wide range of biomedical applications including validation of computational models and imaging techniques, medical device testing, surgery planning, medical education, doctor-patient interaction, etc. Although 3D printing technologies have demonstrated great potential in fabricating patient-specific phantoms, current 3D printed phantoms are usually only geometrically accurate. Mechanical properties of soft tissues can merely be mimicked at small strain situations, such as ultrasonic induced vibration. Under large deformation, the soft tissues and the 3D printed phantoms behave differently. The essential barrier is the inherent difference in the stress-strain curves of soft tissues and 3D printable polymers. This study investigated the feasibility of mimicking the strain-stiffening behavior of soft tissues using dual-material 3D printed metamaterials with micro-structured reinforcement embedded in soft polymeric matrix. Three types of metamaterials were designed and tested: sinusoidal wave, double helix, and interlocking chains. Even though the two base materials were strain-softening polymers, both finite element analysis and uniaxial tension tests indicated that two of those dual-material designs were able to exhibit strain-stiffening effects as a metamaterial. The effects of the design parameters on the mechanical behavior of the metamaterials were also demonstrated. The results suggested that the fabrication of patient-specific tissue-mimicking phantoms with both geometrical and mechanical accuracies is possible with dual-material 3D printed metamaterials. Published by Elsevier B.V.