Non-central heavy-ion collisions at RHIC and LHC can create a strong magnetic field comparable to the QCD scale. Under such extreme environments, hadron properties can be drastically modified. In this talk, I will show our recent theoretical results about properties of hadrons (quarkonia, heavy-light mesons and nucleons) under magnetic field, where various phenomena induced by a magnetic field, such as mass spectra, spin mixing, Landau levels, wave function deformation, and hadron formation time, will be discussed.