Two field experiments were carried out at Gemmeiza Agric. Res. Station, El – Gharbia Governorate during 2010 and 2011 seasons, to study the effect of four NPK fertilizers rates (100 %, 75 %, 50 % and 25 % of recommended rate) and application methods of humic acid on growth of the Egyptian cotton cultivar "Giza 86". The recommended rate of NPK was 45 kg N +22.50 kg P₂O₅ + 24.0 kg K₂O/ fed.. The solutions of humic acid were applied with the concentration of 5 cm³/litre as a soaking seed for 18 h,  50 cm³/litre as soil application twice ,  5 cm³/L as  a foliar application at 40, 55 and 70 days from sowing and without humic acid as a control treatment. Leaf  area index (LAI), total dry weight/plant, crop growth rate (CGR), plant height and number of fruiting branches/plant  were significantly increased by increasing NPK rate from 25 up to 100% of the recommended rate at all sampling dates in both seasons. Also, application of 100% NPK recorded the highest net assimilation rate (NAR) at the first period (79-100 days) in the two seasons. Application  of humic acid solution resulted in a significant increase in all mention growth measurements (except NAR) compared with control treatment in both seasons. Foliar application of humic acid resulted in a significant increase in  leaf  area index, total dry weight/plant, crop growth rate, plant height and number of fruiting branches/plant compared with other application methods in both seasons.  The interaction between NPK rate and humic acid application had a significant effect on LAI, total dry weight/plant, CGR and NAR at the most sampling dates in the two seasons. Plants received 100 or 75% NPK along with foliar application of humic acid produced higher LAI, total dry weight/plant and CGR than those received 25 % NPK and without humic acid at the most sampling dates in both seasons. The relative ranking of the interaction between NPK rate and humic acid application for NAR was inconsistent at the two period in both seasons. None of the interaction had a significant effect on plant height and number of fruiting branches / plant in the two seasons. It can be concluded that 75% NPK and foliar application with humic acid could be recommended for optimum dry matter production of the Egyptian cotton cultivar "Giza 86". This result indicated that foliar application of humic acid can be saved 25% NPK fertilizer without reduce growth of cotton plant.