Differential cross sections for diffractive dijet production
have been measured using e+-p data recorded by H1 in the years 1999 and 2000.
These data are used in combination with the measurements of the inclusive
diffractive structure function F_2^D of H1 to test QCD factorisation
in DIS and to determine the diffractive gluon and quark singlet distribution
by a combined NLO QCD fit.