Split-ring resonators (SRRs) implemented using ferroelectric materials to modify their resonance frequency by means of a tuning voltage are presented for the first time. SRRs have been used to load a microstrip transmission line on a multilayered substrate including a thick film of barium-strontium-titanate (BST) to obtain a tunable stopband response. The characteristics of the BST layer allow the application of 140V as tuning voltage to obtain frequency tunability values of around 12.5. The applied technology is suitable for the fabrication of cost-effective and reliable planar microwave devices. © The Institution of Engineering and Technology 2009.