A bstract The CP asymmetries of seven B − decays to two charm mesons are measured using data corresponding to an integrated luminosity of 9 fb − 1 of proton-proton collisions collected by the LHCb experiment. Decays involving a D *0 or $$ {D}_s^{\ast -} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>D</mml:mi> <mml:mi>s</mml:mi> <mml:mrow> <mml:mo>∗</mml:mo> <mml:mo>−</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> meson are analysed by reconstructing only the D 0 or $$ {D}_s^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>D</mml:mi> <mml:mi>s</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:math> decay products. This paper presents the first measurement of $$ \mathcal{A} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>A</mml:mi> </mml:math> CP ( B − → $$ {D}_s^{\ast -} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>D</mml:mi> <mml:mi>s</mml:mi> <mml:mrow> <mml:mo>∗</mml:mo> <mml:mo>−</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> D 0 ) and $$ \mathcal{A} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>A</mml:mi> </mml:math> CP ( B − → $$ {D}_s^{-} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>D</mml:mi> <mml:mi>s</mml:mi> <mml:mo>−</mml:mo> </mml:msubsup> </mml:math> D ∗ 0 ), and the most precise measurement of the other five CP asymmetries. There is no evidence of CP violation in any of the analysed decays. Additionally, two ratios between branching fractions of selected decays are measured.