Cauliflower and broccoli are important vegetables but have lacking and divergent information about potassium (K) fertilization in soil with a high K content. Two experiments were carried out from 2-1-2010 to 5-20-2010 in Jaboticabal City, São Paulo, Brazil, aiming to evaluate the effect of different K doses (0, 50, 100, 150 and 200 kg ha-1 K2O, in potassium chloride) on the yield of cauliflower ‘Verona’ and broccoli ‘BRO 68’ in Rhodic Eutrudox soil with a high K content. The broccoli and cauliflower responded positively but differently to potassium fertilization. The maximum yield of broccoli (12,476 kg ha-1) was obtained with 160 kg ha-1 K2O, while the yield of cauliflower increased linearly with increasing K dose, yielding 38,285 kg ha-1 with 200 kg ha-1 K2O.