  We say that a set is a multiplicative 3-Sidon set if the equation
$s_1s_2s_3=t_1t_2t_3$ does not have a solution consisting of distinct elements
taken from this set. In this paper we show that the size of a multiplicative
3-Sidon subset of $\{1,2,\dots,n\}$ is at most $\pi(n)+\pi(n/2)+n^{2/3}(\log n
)^{2^{1/3}-1/3+o(1)}$, which improves the previously known best bound
$\pi(n)+\pi(n/2)+cn^{2/3}\log n/\log\log n$.
