The recently synthesized ultrathin diamond nanothreads (NTHs) exhibit a variety of intriguing properties and are probably the most successful of many encouraging applications to be designed as resonators due to their ultrahigh sensitivity and low dissipation. Herein, we report via molecular dynamics that diamond nanothreads possess not only ultrahigh mass sensitivity but also a very high quality factor. On the one hand, the studied diamond nanothreads demonstrate an extreme mass resolution of ∼0.58 yg (1 yg = 10 -24 g), which is almost one order of magnitude higher than that of carbon nanotubes (∼10 yg) with the same length. Moreover, the sensing performance of NTHs is highly tunable owing to their tailorable structures. On the other hand, NTHs exhibit a very low intrinsic energy dissipation and thus a high quality factor which is generally two times that of carbon nanotubes. These intriguing features suggest that diamond nanothreads could be highly attractive candidates for fabricating nano-sized mechanical resonators with outstanding performance. Diamond nanothreads exhibit ultrahigh mass sensitivity and low intrinsic dissipation and have huge potential in sensing applications.