Answer
$(ab-1)(a^2b^2+ab+1)$
Work Step by Step
Using $a^3-b^3=(a-b)(a^2+ab+b^2)$, or the factoring of the difference of $2$ cubes, the factored form of the given expression, $
a^3b^3-1
,$ is \begin{array}{l}\require{cancel}
(ab-1)[(ab)^2+ab(1)+(1)^2]
\\\\=
(ab-1)(a^2b^2+ab+1)
.\end{array}