This work was aimed at studying the effect of wood galactoglucomannan hemicelluloses (HC) on the recovery of copper and molybdenum from a high clay ore. The performance of HC was compared with the results obtained using carboxymethyl cellulose (CMC). Results indicated that HC has a stronger effect than CMC to increase the recovery of Cu from a high clay ore, but a higher depressing effect on the recovery of Mo. At 230 ppm of HC copper recovery increases 7.6 percentage points and Mo recovery decreased 20.7 percentage points respect to samples floated without HC. Thus the use of HC and CMC to improve copper recovery in the flotation high clay copper ore appears to be very promising, but considerations must be done when treating molybdenum rich ores. Due to the fact that HC are semi-amorphous with side hydroxy group on the chain, one possible mechanism of adsorption may be related to hydrogen bonds existing between these hydroxy groups and the surfaces of the clay mineral particles. Further studies that include tests to clarify the mechanisms of adsorption of HC on clay minerals and valuable species, as well as the effect of this reagent on other types of high clay ores are necessary in the future.