ABSTRACT Three experiments, A pot preliminary greenhouse experiment was carried out to choose the most effective levels of cobalt on cauliflower growth and yield. Then Two, field experiments were conducted to evaluate the vegetative growth, heads quantity and quality as well as nutrients content of cauliflower (Brassica oleraceaL.) as affected by using different levels of cobalt. The obtained results showed that the addition of 9 ppm cobalt had a significant positive effect on cauliflower growth, head yield and quality whereas higher concentrations exerted hazards effect.  The content of Mn, Zn and Cu in heads increased with increasing the level of cobalt application. On the other hand, the opposite trend was observed with Fe. Cobalt rate at 9 ppm resulted the greatest values of the vegetative growth, heads yield quantity and quality. Increasing cobalt level more than 9 ppm , the promotive effect reduced.