  We present a method using the SALT2 light curve fitter to determine the
redshift of Type Ia supernovae in the Supernova Legacy Survey (SNLS) based on
their photometry in g', r', i' and z'. On 289 supernovae of the first three
years of SNLS data, we obtain a precision $\sigma_{\Delta z/(1+z)} = 0.022$ on
average up to a redshift of 1.0, with a higher precision of 0.016 for z<0.45
and a lower one of 0.025 for z>0.45. The rate of events with $|\Delta
z|/(1+z)>0.15$ (catastrophic errors) is 1.4%. Both the precision and the rate
of catastrophic errors are better than what can be currently obtained using
host galaxy photometric redshifts. Photometric redshifts of this precision may
be useful for future experiments which aim to discover up to millions of
supernovae Ia but without spectroscopy for most of them.
