To simplify the expression, we can divide each term inside the fraction by the term outside the fraction raised to the second power. This gives us \[\frac{18x^2y^5}{(3xy)^2} = \frac{18x^2y^5}{9x^2y^2}.\] Simplifying further, we can cancel a factor of $9x^2$ from the numerator and denominator, as well as a factor of $y^2$: \[\frac{18x^2y^5}{9x^2y^2} = \frac{2y^3}{1}.\] Therefore, the expression is equivalent to $\boxed{2y^3}$.
