The aim of this study was to determine the combined effects of boron (B) and potassium (K) on metallic cation accumulation, membrane permeability (MP) and growth of tomato (Solanum lycopersicum L.). Four levels of B (0, 5, 10 and 20mg kg(-1)) and two levels of K (0 and 200mg kg(-1)) were applied. B treatments, with or without K, enhanced the MP of leaves and the concentration of metallic cations except for manganese (Mn) and zinc (Zn) concentration as well B concentration. B uptake increased linearly with increasing B treatments. Metallic cation uptakes decreased at the highest B level. Excess B decreased the shoot and root biomass with and without K supply; however, K partially improved the detrimental effect of toxic B on plant growth. It was concluded that supplying K to growth media can be beneficial for alleviating plant growth reduction and imbalances of metallic cations accumulation caused by excess B.