ABSTRACT: Conjugated linoleic acid (CLA) has shown a variety of biologically beneficial effects, such as anticancer, antiatherosclerosis, antidiabetic, immunomodulating, and antiobesity effects. Its effects on reduction of body fat occur with enhancement of lean body mass and body ash; the effects of CLA on bone mass are inconsistent in mice and human studies. We hypothesized that the inconsistency of CLA's effect on ash may be linked to interaction between CLA and dietary calcium levels. We reanalyzed our previous studies, which used mice fed 0.5% CLA-containing diet with regular calcium content (0.5%) or enhanced calcium level (0.66%). Extra calcium in the diet improved CLA's effects on bone mass, particularly in male mice (P= 0.0194); without extra dietary calcium there was no effect of CLA on bone mass. This finding may help improve the efficacy of CLA to be used as a dietary supplement to be used as part of an osteoporosis prevention strategy. Further studies are needed to confirm this observation.