Botanical triterpene celastrol is a candidate drug for the treatment of obesity, except for concerns over the safety in clinical application. The present study was designed to investigate the anti-obesity, anti-inflammatory and toxic activities of celastrol-loaded nanomicelles (nano-celastrol) in diet-induced obese mice. Celastrol was loaded into PEG-PCL nanoparticles, yielding nano-celastrol with optimal size, spherical morphology, good bioavailability, slower peak time and clearance in mice. Nano-celastrol (5 or 7.5 mg/kg/d of celastrol) was administered into diet-induced obese C57BL/6 N male mice for 3 weeks. As result, higher dose nano-celastrol reduced body weight and body fat mass in an equally effective manner as regular celastrol, although lower dose nano-celastrol showed less activity. Similarly, nano-celastrol improved glucose tolerance in mice equally well as regular celastrol, whereas higher dose nano-celastrol improved the response to insulin. As for macrophage M1/M2 polarization in liver, nano-celastrol reduced the expression of macrophage M1 biomarkers (e.g., IL-6, IL-1β, TNF-α, iNOS) in a dose-dependent manner and marginally increased the expression of macrophage M2 biomarkers (e.g., Arg-1, IL-10). Moreover, celastrol could cause anus irritation and disturb intestinal and colonic integrity, whereas nano-celastrol did not cause any injury to mice. Collectively, nano-celastrol represents a translatable therapeutic opportunity for treating diet-induced obesity in humans. Copyright © 2019 Elsevier B.V. All rights reserved.