In all eukaryotic cells, correct segregation of the genetic material during cell division requires proper positioning and alignment of the mitotic spindle with respect to the cell division plane. In the fission yeastSchizosaccharomyces pombe, the spindle is aligned by interphase microtubules during early mitosis , and by astral microtubules and cell shape during late mitosis . However, the mechanisms that control spindle alignment in mid-mitosis are not known. The lack of such a control could lead to extensive spindle rotation and misalignment, which, in turn, would result in chromosome mis-segregation if spindle elongation were impaired . Here, we show that the association of mitochondria with the spindle poles reduces spindle rotation. In wild-type cells, spindles with associated mitochondria did not rotate as much as free spindles. In a mutant lacking the centrosomin- related protein Mto1p, the association between mitochondria and spindles was reduced and the spindles rotated more than those in wild-type cells. We propose that there is a symbiotic relationship between mitochondria and the mitotic spindle, in which close association between the two organelles facilitates the positioning of both: while the spindle helps to segregate mitochondria equally among the nascent daughter cells , mitochondria decrease spindle rotation and thus promote spindle alignment.