A novel approach to fabricating highly-oriented, nm-scale potassium titanate K2Ti6O13 rod arrays on titanium substrates was demonstrated. The fabrication process was template-free, and simply involved coating the titanium substrates with pulverized potassium metaborate and its derivatives, and subsequent heating at 700°C for 5 h. When the samples were soaked in hot water, the coating layers were readily removed, leaving an array of titanate crystallites on the titanium substrates. Even the slightest change in the composition of the potassium borates resulted in various microstructures, while K2O·1.03B2O 3 yielded highly-oriented nanorod arrays of K2Ti 6O13. Bioactivity of the as-achieved nanorod arrays was proved by the deposition of apatite in simulated body fluid (SBF: Kokubo solution). When soaked in SBF, the K2Ti6O13 nanorod arrays deposited apatite within one day accompanying the release of potassium ions from the crystallites into SBF and the arrays were covered with apatite layers in three days. Ion exchange between the potassium ions in the crystal and calcium ions in SBF is proposed as the mechanism operative to favor the deposition of apatite.