A bstract Using pp collisions corresponding to 3 fb −1 integrated luminosity, recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, the ratio of branching fractions $$ \mathrm{\mathcal{B}}\left({\Lambda}_b^0\to \psi (2S)\Lambda \right)/\mathrm{\mathcal{B}}\left({\Lambda}_b^0\to J/\psi \Lambda \right)=0.513\pm 0.023\left(\mathrm{stat}\right)\pm 0.016\left(\mathrm{syst}\right)\pm 0.011\left(\mathrm{\mathcal{B}}\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ℬ</mml:mi> <mml:mfenced> <mml:mrow> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>b</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:mo>→</mml:mo> <mml:mi>ψ</mml:mi> <mml:mfenced> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>S</mml:mi> </mml:mrow> </mml:mfenced> <mml:mi>Λ</mml:mi> </mml:mrow> </mml:mfenced> <mml:mo>/</mml:mo> <mml:mi>ℬ</mml:mi> <mml:mfenced> <mml:mrow> <mml:msubsup> <mml:mi>Λ</mml:mi> <mml:mi>b</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:mo>→</mml:mo> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> <mml:mi>Λ</mml:mi> </mml:mrow> </mml:mfenced> <mml:mo>=</mml:mo> <mml:mn>0.513</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.023</mml:mn> <mml:mfenced> <mml:mi>stat</mml:mi> </mml:mfenced> <mml:mo>±</mml:mo> <mml:mn>0.016</mml:mn> <mml:mfenced> <mml:mi>syst</mml:mi> </mml:mfenced> <mml:mo>±</mml:mo> <mml:mn>0.011</mml:mn> <mml:mfenced> <mml:mi>ℬ</mml:mi> </mml:mfenced> </mml:math> is determined. The first uncertainty is statistical, the second is systematic and the third is due to the external branching fractions used.