Abstract Background Maternal diabetes is associated with morphological placental abnormalities and foeto‐placental impairments. These alterations are linked with a dysregulation of the activity of matrix metalloproteinases (MMPs). We investigated the action of 15deoxyΔ 12,14 prostaglandin J 2 (15dPGJ 2 ), a natural ligand of the peroxisome proliferator activated receptor (PPAR) γ, on MMP‐2 and MMP‐9 activities and tissue inhibitors of matrix metalloproteinases (TIMP) levels in foetuses and placentas from diabetic rats. Materials and methods Diabetes was induced in rat neonates by a single streptozotocin administration (90 mg kg −1 s.c.). At 13·5 days of gestation, foetal and placental homogenates were prepared for the determination of PPARγ levels (western blot) and 15dPGJ 2 concentration (enzyme‐immunoassay), whereas the in vitro effect of 15dPGJ 2 (2 μM) was evaluated on placental and foetal MMPs and TIMP activities (zymography and reverse zymography), nitrate/nitrite concentrations (Griess method) and thiobarbituric acid reactive substances (TBARS). Results PPARγ was increased while 15dPGJ 2 was decreased in placentas and foetuses from diabetic rats. 15dPGJ 2 additions were able to reduce the high activities of MMP‐2 and MMP‐9 present in diabetic placental tissues. 15dPGJ 2 additions reduced MMP‐2 activity in control and diabetic foetuses. TIMP‐3 levels were decreased in diabetic placentas and 15dPGJ 2 was able to enhance them to control values. Nitrates/nitrites and TBARS, metabolites of MMPs activators, were increased in the diabetic placenta and reduced by 15dPGJ 2 . Conclusions This study demonstrates that 15dPGJ 2 is a potent modulator of the balance between MMP activities and TIMP levels, which is needed in the correct formation and function of the placenta and foetal organs.