This paper presents a dual band slotted rectangular patch antenna with partial ground for 2.4/5 GHz wireless local area network (WLAN) application. The antenna operates at 2.4 GHz and 5.2 GHz frequency which are reserved for IEEE802. 11b/g and IEEE802. 11a WLAN standard. The substrate used for antenna design is FR4 substrate with relative permittivity of 4.4 and loss tangent of 0.02, which is a inexpensive and widely used printed circuit board (PCB). The overall dimension of antenna is 50× 50× 1.6 mm3, where 1.6 mm is the thickness of FR4 substrate. Dimension of the patch, rectangular slot and ground plane are 34mm× 20mm, 32.5 mm× 10mm and 50mm× 8mm respectively. The slotted patch is directly edge-fed by 50-Ω microstrip line. The effective omni-directional/directional radiation pattern and impedance bandwidth, return-loss, VSWR, and gain have been investigated using computer simulation on HFSS. Using this antenna, impedance bandwidths (/S11/<-10dB) of 9.05% and 18.12% were achieved at operating frequencies 2.4 GHz and 5.2 GHz, with gains of 3.01 dBi and 6.36 dBi, respectively. The 10-dB impedance bandwidth (2.23-2.44 and 4.99-6.0 GHz) completely meets the WLAN application requirements.