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.