Piezoelectrets (or piezoelectric polymer foams) are porous piezoelectric materials with a wide range of applications particularly sensing. They have been successfully fabricated different techniques such as foaming, and fusion assembled of preformed structures. These fabrication techniques face several challenge issues such as limited structure design space and structural uniformity control. In this study we demonstrated direct 3D printing of piezoelectrets with designed pore structure using fusion deposition modeling (FDM). The feasible printing conditions was first explored using a response surface methodology to address challenges unique to piezoelectret structures. Subsequently, two types of prototypes were successfully printed with a maximum piezoelectric coefficient d33 ~1000pC/N achieved. By varying the structure design, performance of the piezoelectrets can be customized over a broad range that was not attainable via other technologies. We finally demonstrated the sensing application of the printed piezoelectret sensors.