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The MIPSGAL 24 $\mu$m Galactic Plane Survey has revealed more than 400compact-extended objects. Less than 15% of these MIPSGAL bubbles (MBs) areknown and identified as evolved stars. We present Spitzer observations of 4 MBsobtained with the InfraRed Spectrograph to determine the origin of the mid-IRemission. We model the mid-IR gas lines and the dust emission to infer physicalconditions within the MBs and consequently their nature. Two MBs show adust-poor spectrum dominated by highly ionized gas lines of [\ion{O}{4}],[\ion{Ne}{3}], [\ion{Ne}{5}], [\ion{S}{3}] and [\ion{S}{4}]. We identify themas planetary nebulae with a density of a few 10$^3\ \rm{cm^{-3}}$ and a centralwhite dwarf of $\gtrsim 200,000$ K. The mid-IR emission of the two other MBs isdominated by a dust continuum and lower-excitation lines. Both of them show acentral source in the near-IR (2MASS and IRAC) broadband images. The firstdust-rich MB matches a Wolf-Rayet star of $\sim 60,000$ K at 7.5 kpc with dustcomponents of $\sim170$ and $\sim1750$ K. Its mass is about $10^{-3}\\rm{M_\odot}$ and its mass loss is about $10^{-6}\ \rm{M_\odot/yr}$. The seconddust-rich MB has recently been suggested as a Be/B[e]/LBV candidate. The gaslines of [\ion{Fe}{2}] as well as hot continuum components ($\sim300$ and$\sim1250$ K) arise from the inside of the MB while its outer shell emits acolder dust component ($\sim75$ K). The distance to the MB remains highlyuncertain. Its mass is about $10^{-3}\ \rm{M_\odot}$ and its mass loss is about$10^{-5}\ \rm{M_\odot/yr}$.

Spitzer/IRS investigation of MIPSGAL 24 microns compact bubbles