The present study investigates the influence of different plasma treatments on the tensile characteristics of lyocell fibers and the interfacial interactions of lyocell fibers in a poly(lactic acid) matrix. For the investigations, the fibers were coated by an amine-functional, nanoporous layer (a-C:H:N) using a gaseous mixture of NH3:C2H4 of 1:1 and 5:3, respectively, an oxygen-functional layer (a-C:H:O) with CO2:C2H4 and CO2 posttreatment, or an oxygen-functional layer (a-C:H:O) comprising hydroxyl groups with H2O:C2H4 and H2O posttreatment. As reference, uncoated fibers and fibers coated with a crosslinked, amorphous hydrocarbon layer (a-C:H) without functional group incorporation were investigated. While the different treatments maintained the tensile strength of the lyocell fibers, which were all in the range between 295 and 338 N/mm2, the interfacial shear strength, measured by the pull-out test, was clearly influenced. The best improvement of the fiber/matrix adhesion was obtained by a plasma treatment with a mixture of water vapor and ethylene resulting in an interfacial shear strength of 17.8 N/mm2 in comparison to the untreated lyocell fiber with 10.3 N/mm2. Amine-functional plasma polymers (a-C:H:N) were also found to be suitable for adhesion-promoting interlayers on lyocell fibers in poly(lactic acid). (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013