Abstract: The Cabibbo-suppressed decay Lambda b0</mml:msubsup>-> chi (c1)p(-) is observed for the first time using data from proton-proton collisions corresponding to an integrated luminosity of 6 fb(-1), collected with the LHCb detector at a centre-of-mass energy of 13 TeV. Evidence for the Lambda b0</mml:msubsup>-> chi (c2)p(-) decay is also found. Using the Lambda b0</mml:msubsup>-> chi (c1)pK(-) decay as normalisation channel, the ratios of branching fractions are measured to be<disp-formula id=“Equa”><mml:mtable displaystyle=“true”><mml:mtr><mml:mtd><mml:mfrac>B<mml:mfenced close=“)” open=“(”>Lambda b0</mml:msubsup>-> chi c1p pi-</mml:mfenced>B<mml:mfenced close=“)” open=“(”>Lambda b0</mml:msubsup>-> <mml:msub>chi c1pK-</mml:mfenced></mml:mfrac>=<mml:mfenced close=“)” open=“(”>6.59 +/- 1.01 +/- 0.22</mml:mfenced>x10-2,</mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mfrac>B<mml:mfenced close=“)” open=“(”>Lambda b0 -> <mml:msub>chi c2p pi-</mml:mfenced>B<mml:mfenced close=“)” open=“(”>Lambda b0 -> <mml:msub>chi c1p pi-</mml:mfenced></mml:mfrac>=0.95 +/- 0.30 +/- 0.04 +/- 0.04,</mml:mtd></mml:mtr><mml:mtr><mml:mtd><mml:mfrac>B<mml:mfenced close=“)” open=“(”>Lambda b0 -> <mml:msub>chi c2pK-</mml:mfenced>B<mml:mfenced close=“)” open=“(”>Lambda b0 -> <mml:msub>chi c1pK-</mml:mfenced></mml:mfrac>=1.06 +/- 0.05 +/- 0.04 +/- 0.04,</mml:mtd></mml:mtr></mml:mtable><graphic position=“anchor” xmlns:xlink=“http://www.w3.org/1999/xlink” xlink:href=“13130202115658ArticleEqua.gif”></graphic></disp-formula><p id=“Par2”>where the first uncertainty is statistical, the second is systematic and the third is due to the uncertainties in the branching fractions of chi (c1,2)-> J/psi gamma decays.<fig id=“Figa” position=“anchor”><graphic position=“anchor” specific-use=“HTML” mime-subtype=“JPEG” xmlns:xlink=“http://www.w3.org/1999/xlink” xlink:href=“MediaObjects/13130202115658FigaHTML.jpg” id=“MO1”></graphic