Abstract The effect of grain size and titanium content on the flow stress was studied at room temperature for solution-treated CuTi alloys. It was found that the Hall-Petch relation is valid for the four compositions tested: Cu-1.5 wt% Ti, Cu-2.7 wt% Ti, Cu-4.5 wt% Ti and Cu-5.4 wt% Ti alloys. The Hall-Petch constants σ o ϵ and k ϵ in the equation: σ ϵ = σ oϵ + k ϵ · d − 1 2 increase with increasing strain as well as Ti content. σ o ϵ and k ϵ are related to strain (ϵ) in such a way that σ o ϵ is proportional to ϵ for 1.5 and 2.7 wt% Ti alloys, and ϵ 3 2 for 4.5 and 5.4 wt% Ti alloys, while k ϵ is proportional to ϵ 1 2 for all four alloys. Considerable increase in yield strength has been observed with increasing Ti content at a common grain size. The increase in yield strength in high Ti content (4.5 and 5.4 wt% Ti) alloys is associated with solid solution strengthening, grain size strengthening as well as fine scale precipitation, first as a mottled structure in Cu-4.5 wt% Ti, and then as a metastable, body-centred tetragonal Cu 4Ti phase, β′ in Cu-5.4 wt% Ti alloy, formed during quenching itself.