Abstract: A miniaturized ultra-wideband butterfly printed log-periodic antenna for microwave medical imaging systems is de-signed. An inductive stub is loaded at the beginning of the feed line to improve the impedance matching of the antenna, and butter-fly and U-shaped patch structures are loaded on the conventional printed log-periodic antenna to expand the bandwidth and realize the miniaturization of the antenna. The size of the antenna is 0. 300 λ×0. 280 λ×0. 007 λ(f = 1. 12 GHz), the measured working band of the antenna with S11<-10 dB is 1. 12 GHz~ 4 GHz, and the maximum measured gain reaches 6 dBi. The measured direc-tional map of the antenna achieves directional radiation in the operating band with good radiation effect, and the antenna can be ap-plied to medical fields such as microwave brain detection system.