Magnetic microbeads have recently been the subject of much study because of their potential applications in microfluidic systems which facilitate mixing, labeling, separation, and transport in lab-on-a-chip devices. To manipulate the microbeads chain swimming in the low-Reynolds-number environment, various magnetic actuation methods have been employed to obtain the higher propulsive efficiency for the locomotion in the viscous fluid. A flexible flagellum is arguably the simplest mechanism to duplicate as it is a 1-D structure. However, a challenge to create the stable planar beating motion for propulsion generation is to fabricate the magnetic flagellum simultaneously flexible and stable structure at a microscale. Driven by this motive, this paper has constructed a series of artificial flexible flagella composed of self-assembled beads whose flexibility was probed in the influence of an oscillating external field. To effectively use the oscillating magnetic flagellum for the application in the microfluidic system, the measurement of the maximum dimensionless curvature (<inline-formula> <tex-math notation="LaTeX">C_{\mathbf {max}} </tex-math></inline-formula>) and bending rigidity for the flexible microchain are experimentally and theoretically investigated in this paper. At a lower frequency of <inline-formula> <tex-math notation="LaTeX">f=1 </tex-math></inline-formula> Hz, the value of <inline-formula> <tex-math notation="LaTeX">C_{\mathbf {max}} </tex-math></inline-formula> of the flagellum increases linearly with the applied field intensity and gets higher then declines with the increase of the flagellum's length. On the other hand, the longer flagellum has the more stable flexible structure at a higher frequency of <inline-formula> <tex-math notation="LaTeX">f=3 </tex-math></inline-formula>-7 Hz, which resists the amplitude and enhances the deformation of the longer flagellum.