In this paper, microstrip-fed slot antennas with suppressed harmonics are proposed. To obtain this operation, conductor lines connected with ground plane are inserted in slot antennas. To verify the validation of the proposed antennas, the equivalent circuit analysis is presented. Also, the miniaturization and bandwidth enhancement of the antenna for various applications are achieved and analyzed through parameter study. From the measured return losses, input impedances, and radiation patterns, it is shown that the proposed antennas offer excellent harmonic suppression characteristic in harmonic bandwidth including the second and third harmonic frequencies.