The effect of grain size and titanium content on the flow stress was studied at room temperature for solution-treated Cu-Ti 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 constant σ o ε and k ε in the equation: σ o ε = σ o ε +k ε d - 1 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 for 4.5 and 5.4 wt% Ti alloys, while k ε is proportional to ε 1 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 4 Ti phase, β in Cu-5.4 wt% Ti alloy, formed during quenching itself.