We report a measurement of the B0s lifetime in the semileptonic decay channel B0s→D−sμ+νX (and its charge conjugate), using approximately 0.4 fb−1 of data collected with the D0 detector during 2002–2004. Using 5176 reconstructed D−sμ+ signal events, we have measured the B0s lifetime to be τ(B0s)=1.398±0.044(stat)+0.028−0.025(syst) ps. This is the most precise measurement of the B0s lifetime to date.Received 24 April 2006DOI:https://doi.org/10.1103/PhysRevLett.97.241801©2006 American Physical Society