In rodents and some other mammals, partial pneumonectomy (PNX) of adult lungs results in rapid compensatory lung growth. In the past, quantification of compensatory lung growth and realveolarization could only be accomplished after killing the animal, removal of lungs, and histologic analysis of lungs at single time points. Hyperpolarized (3)He diffusion magnetic resonance imaging (MRI) allows in vivo morphometry of human lungs; our group has adapted this technique for application to mouse lungs. Through imaging, we can obtain maps of lung microstructural parameters that allow quantification of morphometric and physiologic measurements. In this study, we employed our (3)He MRI technique to image in vivo morphometry at baseline and to serially assess compensatory growth after left PNX of mice. (1)H and hyperpolarized (3)He diffusion MRI were performed at baseline (pre-PNX), 3-days, and 30-days after PNX. Compared with the individual mouse's own baseline, MRI was able to detect and serially quantify changes in lung volume, alveolar surface area, alveolar number, and regional changes in alveolar size that occurred during the course of post-PNX lung growth. These results are consistent with morphometry measurements reported in the literature for mouse post-PNX compensatory lung growth. In addition, we were also able to serially assess and quantify changes in the physiologic parameter of lung compliance during the course of compensatory lung growth; this was consistent with flexiVent data. With these techniques, we now have a noninvasive, in vivo method to serially assess the effectiveness of therapeutic interventions on post-PNX lung growth in the same mouse.