A ultra-wideband microwave absorber (UWMA) combining frequency-selective surfaces (FSS) and dielectric layers is proposed. FSS patterns are printed by inkjet on dielectric layers using a resistive magnetic ink made of suspended carbon nanotubes decorated with $${\text {Fe}}_3{\text {O}}_4$$ nanoparticles. The UWMA exhibits a huge fractional bandwidth of 140%, corresponding to reflectivity lower than − 10 dB and absorption higher than 90%, observed from 7 GHz to 43 GHz, meaning a 36 GHz bandwidth, for a thickness of only 0.26 $$\lambda$$. This performance is achieved through a proper selection of FSS surface resistance, tuned by the number of printed layers. Excellent agreement is observed between designed and measured low reflectivity and high absorption.