  We present GALEX UV observations of a sample of Low Surface Brightness (LSB)
galaxies for which HI data are available, allowing us to estimate their star
formation efficiency. We find that the UV light extends to larger radii than
the optical light (some galaxies, but not all, look similar to the recently
discovered XUV-disk galaxies). Using a standard calibration to convert the UV
light into star formation rates, we obtain lower star formation efficiencies in
LSB galaxies than in high surface brightness galaxies by about one order of
magnitude.
  We show however that standard calibrations may not apply to these galaxies,
as the FUV-NUV color obtained from the two GALEX bands (FUV and NUV;
lambda_eff= 1516 and 2267 A, respectively) is redder than expected for star
forming galaxies. This color can be interpreted as a result of internal
extinction, modified Initial Mass Function or by star formation histories
characterized by bursts followed by quiescent phases. Our analysis favors this
latter hypothesis.
