  We report on observations of the superbubbles (SBs) N11 and N51D in the Large
Magellanic Cloud (LMC) with Suzaku and XMM-Newton. The interior of both SBs
exhibits diffuse X-ray emission, which is well represented by thin thermal
plasma models with a temperature of 0.2-0.3keV. The presence of nonthermal
emission, claimed in previous works, is much less evident in our careful
investigation. The 3-sigma upper limits of 2-10keV flux are
3.6*10^{-14}ergs/cm^2/s and 4.7*10^{-14}ergs/cm^2/s for N11 and N51D,
respectively. The previous claims of the detection of nonthermal emission are
probably due to the inaccurate estimation of the non X-ray background. We
conclude that no credible nonthermal emission has been detected from the SBs in
the LMC, with the exception of 30 Dor C.
