An ultra wideband filter is provided that filters an input signal using a pair of cross-coupled transistors with a small size and small power consumption. The ultra wideband filter includes a reference current generator unit generating a reference current using a bias signal of a predetermined level, a transconductor unit that is biased by the reference current and converts a predetermined input voltage into a current of a predetermined amount to output the current if the input voltage is applied thereto, and a filter unit that outputs a predetermined output voltage corresponding to the output current of the transconductor unit using a plurality of cross-coupled transistors and capacitors. The filter unit may include cross-coupled nMOS and pMOS transistors, and first and second capacitors respectively connected to respective drain terminals of the nMOS and pMOS transistors. Accordingly, the ultra wideband filter can be designed in a minimum size.