  Low-temperature magnetic properties of both classical and quantum dimerized
ferromagnetic spin chains are studied. It is shown that at low temperatures the
classical dimerized model reduces to the classical uniform model with the
effective exchange integral $J_{0}=J(1-\delta^{2})$, where $\delta$ is the
dimerization parameter. The partition function and spin correlation function
are calculated by means of mapping to the continuum limit, which is justified
at low temperatures. In the continuum limit the calculation of the partition
function and spin correlation function is reduced to the eigenvalue problem of
quantum rotator in gravitational field. Quantum model is studied using
Dyson-Maleev representation of the spin operators. It is shown that in the
long-wavelength limit the Hamiltonian of the quantum dimerized chain reduces to
that of the uniform ferromagnetic chain with the effective exchange integral
$J_{0}=J(1-\delta^{2})$. This fact implies that the known equivalence of the
low-temperature magnetic properties of classical and quantum ferromagnetic
chains remains for the dimerized chains. The considered model can be
generalized to include the next-neighbor antiferromagnetic interaction.
