Résumé : The mean lifetime of the 3ΛH hypernucleus has been estimated in nuclear emulsion using the (π-+1H+2H) decays both at rest and in flight. The result, τ(3ΛH) = (1.28-0.26+0.35) · 10-10 sec, is significantly lower than another recent experimental value [5] and the theoretical predictions. A possible explanation of the discrepancy with the theoretical predictions is briefly discussed. © 1970.