Recent communication requirements continue to push for more bandwidth capabilities for antenna systems. In order to communicate with tags from different countries, the RFID system requires a separate set of antennas for reader application. As a result, our environments are infected by diverse kinds of antennas. This compact multiband antenna is designed to obtain dual-band RFID reader operation at the UHF bands of 860MHz-960MHz and free ISM bands of 2.45 GHz. Therefore, this antenna is design to reduce the set of antenna in RFID system. The dual band characteristic of this antenna is achieved by incorporating another slot to the single slot. The center frequencies of these bands are controlled by the electrical length of these slots. It is a rectangular patch antenna consists with two steps, an inverse phi shape slot on the patch, and a partial ground plane. This antenna is designed with the benefit of low cost, ease of manufacture and low profile. A moderate gain is achieved. With the omnidirectional radiation pattern characteristic, this antenna will suit for portable RFID reader application.