The ageing precipitation sequence and the relationship between microstructure and tensile properties of metastable β titanium alloy Ti-6Cr-5Mo-5V-4Al during solution and ageing were investigated. Ageing from 400 to 450 °C, isothermal ω phase (ω_iso) precipitated in the alloy, resulting in high hardening and brittle fracture. After ageing at 450-500 °C, ω_iso phase was gradually replaced by secondary α phase (α_s) with the ageing time increasing. At higher ageing temperature (580-600 °C), ω_iso precipitation was suppressed, and α_s phase precipitated directly from β phase. The yield strength of sample aged at 450 °C for 12 h was 1368 MPa and the elongation was 5.5% due to ω_iso precipitation. The yield strength of sample aged at 600 °C for 12 h was 1108 MPa and the elongation was improved to 15.4% due to the precipitation and coarsening of α_s phase.