We prove the $L^{p}$ boundedness of the Marcinkiewicz integral operators $μ_{Ω}$ on $ℝ^{n₁}× ⋯ ×ℝ^{n_{k}}$ under the condition that $Ω ∈ L(log L)^{k/2}(𝕊^{n₁-1}× ⋯ ×𝕊^{n_{k}-1})$. The exponent k/2 is the best possible. This answers an open question posed by Y. Ding.