The conformal coating of ultra-thin aluminum alkoxide (alucone) polymer films on primary silica and titania nanoparticles using molecular layer deposition (MLD) in a fluidized bed reactor from 100 to 160 degrees C is described. In situ mass spectrometry revealed that the growth of alucone MLD films was self-limiting as a function of the individual trimethylaluminum and ethylene glycol exposures. The composition and highly conformal alucone films throughout the surface of both silica and titania nanoparticles were confirmed. The highest growth rate was observed at the lowest sample temperature. Primary nanoparticles were coated individually despite their strong tendency to aggregate during fluidization. Based on the results of chemical and thermogravimetric analysis, the value of x in the formula of Al(OCH2CH2O)(x) was estimated to be 1.9. The calculated film density slightly increased from 2.0 +/- 0.1 to 2.2 +/- 0.1 g/cm(3) with the increasing of temperature from 100 to 160 degrees C. (C) 2009 American Institute of Chemical Engineers AIChE J, 55: 1030-1039, 2009