Abstract: Hyperbranched polyether HBPO-star-PEO (HSP, HBPO: hyperbranched poly(3-ethl-3-oxetanemthanol; PEO: polyethyleneglycol)) with different PEO arm lengths were synthesized by cationic ring-opening polymerization. A series of ultrasound contrast agents (UCA) were prepared using HSP as shell materials and SF₆ as inner gas, which were named as HSP-UCA. The size, micromorphology, SF₆ concentration and in vitro/in vivo ultrasound imaging effect of HSP-UCA were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), gas chromatography-mass spectrometry (GC-MS), and ultrasound imaging instrument. The results showed that analogous to the effect of PEO arm length on the stability of the vesicles, the stability of UCA increased with the PEO arm length, resulting in an increase in its concentration. When the PEO arm length was increased to 10, high concentration of HSP₁₀-UCA was obtained with an average size of 517.3 nm, the SF₆ volume fraction of 9.12 ×10⁻³ and the in vitro ultrasound half-life of 3−5 min. in vivo Ultrasound test of HSP₁₀-UCA in rabbit heart showed good ultrasound contrast effect. Before the injection of nano-scale HSP₁₀-UCA, the ultrasound echo signal inside the heart was very low and the internal structure could not be observed by ultrasound imaging. However after intravenous injection of HSP₁₀-UCA, the rabbit heart was quickly perfused, its internal structure was slowly appeared. The average ultrasound contrast duration of HSP₁₀-UCA was 50−60 s. The above results indicate that the nano-scale HSP₁₀-UCA is an excellent ultrasound contrast agent and its good ultrasound contrast effect will be beneficial to its future applications in the ultrasound imaging of tumor tissues.