The discovery of natural ferromagnetic resonance (NFMR) [1] in amorphous microwires was preceded by their study with standard FMR methods [2]. A microwire was considered as ferromagnetic cylinder with small radius rm. For its characterization we introduce following parameters: 1. The depth of the skin layer is:  formula  is the effective magnetic permeability, and σ is the microwire electrical conductivity. In the case of our magnetic microwires, with the relative permeability ׀μ׀ near resonance of the order 102, (ω ~ (1- 10) GHz) δ changes from 1 up to 4 μm. 2. The size of the domain wall is: Δ = π( A/K) 1/2 ~ 10 – 0,1 μm , (1b) where A is the exchange constant and K is the energy anisotropy of microwire. 3. Radius of single domain (according to Brown theory) is:formulawhere Ms is the saturation magnetization of microwire. According to [1] the frequency of the NFMR is:formulawhere is the gyromagnetic ratio ( ~ 3 МHz/Oe) . The anisotropy field is He ~ 3λσ/Ms, where λ is the magnetostriction constant; and σ is the effective residual stress originated from the fabrication procedure (see [1, 2]). If r m < δ , we have:formulaIf r m > δ , the formula for the NFMR frequency can be written as (see [2]):formulaSince skin penetration depth of microwave field in metallic wire is relatively small in comparison with its diameter the resonant frequency of FMR can be determined by means of Kittel formula (eq.(4)). Taking into account magnetoelastic stress field [1, 2], for thin film magnetized parallel to the surface, we can obtain:formulawhere H is resonant field of FMR; X Y Z N′ , N′ , N′ are components of tensor of effective demagnetizing factors in case of magnetoelastic stress [2]. For the frequency of NFMR in simple approximation formula (5) can be written as: