Root activity measured with triphenyl tetrazolium chloride (TTC) is related with nicotinamide adenine dinucleotide (NAD) dehydrogenase during aerobic respiration of roots (Shimada 1969). Exogenous phytohormones applied significantly affected root activity. Single applied GA3 and combined treatment applications of IAA x GA3 x Z at 80 DAT and IAA x GA3 x Z at 90 DAT stimulated high level of root activity. Present results agree with the finding of Atkins (1992), Clark et al., (1992), who reported that plant growth regulator (PGR-IV) that consists of gibberellic acid and synthetic indolebutyric acid (auxin derivative) increased root mass and root activity. The result of this present study also includes zeatin (cytokinin) as a phytohormone that could be used to stimulate cotton root activity. Nevertheless, Xin cotton variety possessed higher root activity than Zhong cotton variety this could be due as a result of differences in their genetic makeup.