The mutual coupling of planar inverted F-antennas (PIFA) on a small ground plane is investigated. Dual band 900MHz + 1800/2000MHz PIFA, 2.4 GHz PIFA and 4.9–5.9GHz PIFA were used in the study. These antennas were placed on the 120mm×50mm ground plane in different orientations. From simulations, it has been observed that the mutual coupling becomes quite significant when antennas were placed very near to each other, even when they were operating at different bands. The simulations were validated by measurements.