  In this paper, we prove a $Tb$ theorem on product spaces $\Bbb R^n\times \Bbb
R^m$, where $b(x_1,x_2)=b_1(x_1)b_2(x_2)$, $b_1$ and $b_2$ are para-accretive
functions on $\Bbb R^n$ and $\Bbb R^m$, respectively.
