The preparation of nanofluids with good suspending stability is an important premise for further scientific research and engineering application. However, previous studies mainly focused on the stability of nanofluids in static situation without any flow, and seldom discussed the suspending stability of nanofluids in flow. The objective of this study is to investigate the suspending stability of nanofluids in flow using TiO 2 -water nanofluids flowing through a circular tube as an example. The study uses the centrifugal sedimentation weight of supernatant suspending solution to characterize the stability of nanofluids. The bigger centrifugal sedimentation weight represents the better stability. This study also characterization of particle size distribution of nanofluids by Malvern laser particle size analyzer. In the present experiment conditions, TiO 2 -water nanofluids with the mass fraction of 0.5% are driven by a peristaltic pump and flows through a circular tube with 4.8 mm inner diameter. In the present experimental conditions, the volume flow rate of TiO 2 -water nanofluids is slightly lower than that of pure water. The size distribution of nanoparticle in fluid after circulating flow 2 hours behaves more uniformly than that in a fluid after maintaining static situation 2 hours. with the increasing of Reynolds number of fluid in circulating flow, the suspending stability of nanofluids in circulating flow is significantly higher that that in static situation. When the Reynolds number is up to 2000, the suspending status of nanoparticles in the base fluid is nearly the same as the initial status of sample before circulating. Despite its preliminary, this work demonstrates that the flow pattern is one of influence factors on the suspending stability of nanofluids, which should not be ignored in the study of the suspending stability and heat transfer performance of nanofluids. This study may give some inspiration for further research on relative fields such as the preparation of nanofluids for heat transfer enhancement and so on.