In order to increase the power density and improve the stability of the grid-connected inverter, an integrated unit for an LCL filter and a transformer is proposed by adopting the planar printed circuit board (PCB) integration technique. The structure of the integrated unit is introduced, the designs of the parameters are presented, and the flux analysis is provided. Then, a prototype of the integrated unit for a 600 W grid-connected inverter is built and tested. Finally, the experimental results prove the feasibility of the theory.