Electronic Journal of Differential Equations, Vol. 2022 (2022), No. 48, pp. 1-23. Title: Cauchy problems for chemotaxis systems with chemo attractant and repellent Authors: Aesha Lagha (Zawia University, Zawia, Libya}) Harumi Hattori (West Virginia Univ., Morgantown, WV, USA) Abstract: We study the existence of global solutions and their asymptotic behavior for a chemotaxis system with chemo-attractant and repellent in three dimensions. To accomplish this, we use the Fourier transform and energy method. First, we establish Lq time-decay for the linear homogeneous system using Fourier transform and finding Green's matrix. Then, we find Lq time-decay for the nonlinear system using the Duhamel's principle and the time-weighted estimates. Submitted September 4, 2021. Published July 05, 2022. Math Subject Classifications: 35Q31, 35Q35, 35Q92, 76N10. Key Words: Energy method; a priori estimates; Fourier transform; time-decay rates.