"At 02:17:30.61 UT on 28 July 2010, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 100728A (trigger 301976252 / 100728095), which was also detected by the Swift-BAT (Cannizzo et al. 2008, GCN 11004) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 58.6 degrees. The GBM light curve shows a multi-peaked structure with a duration (T90) of about 162.9 +/- 0.9 s (50 - 300 keV). The time-averaged spectrum from T0-8.192 s to T0+191.491 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -0.76 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 353.7 +/- 6.7 keV (Castor C-STAT 3540 for 727 d.o.f.) . The event fluence (8-1000 keV) in this time interval is (1.291 +/- 0.008)E-04 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+80.2 s in the 8-1000 keV band is 10.8 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well (Castor C-STAT 3537 for 726 d.o.f.) with Epeak= 344.3 +9.1/-7.9 keV, alpha = -0.75 +/- 0.01 and beta = -3.04 +0.23/-0.57. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."