We report exciton spin relaxation dynamics in colloidal wurtzite and zinc blende CdSe quantum dots measured using ultrafast cross-polarized heterodyned transient grating spectroscopy. The zinc blende ( cubic base) quantum dots have a simpler fine structure as compared to wurtzite ( hexagonal base) due to differences in the crystal field splitting. Faster exciton spin relaxation dynamics are observed in the zinc blende quantum dots. (C) 2010 Elsevier B. V. All rights reserved.