Context :

Aims : We observed the high energy peaked BL Lac object PKS 0548 - 322 ( BZB J0550 - 3216 ) with Swift to study the temporal and spectral properties of its synchrotron emission simultaneously in the Optical , Ultraviolet and X-ray energy bands .

Methods : We carried out a spectral analysis of 5 Swift XRT and UVOT observations of PKS 0548 - 322 over the period April - June 2005 .

Results : The X-ray flux of this BL Lac source was found to be approximately constant at a level of F _ { ( 2 - 10 ~ { } { \mathrm { k } eV } ) } \simeq 4 \times 10 ^ { -11 } erg cm ^ { -2 } s ^ { -1 } , a factor of 2 brighter than when observed by Beppo SAX in 1999 and close to the maximum intensity reported in the Einstein Slew Survey .
The very good statistics obtained in the 0.3-10 keV Swift X-ray spectrum allowed us to detect highly significant deviations from a simple power law spectral distribution .
A log-parabolic model describes well the X-ray data and gives a best fit curvature parameter of 0.18 and a peak energy in the Spectral Energy Distribution of about 2 keV .
The UV spectral data from Swift UVOT join well with a power law extrapolation of the soft X-ray data points suggesting that the same component is responsible for the observed emission in the two bands .
The combination of synchrotron peak in the X-ray band and high intensity state confirms PKS 0548 - 322 as a prime target for TeV observations .
X-ray monitoring and coordinated TeV campaigns are highly advisable .

Conclusions :