This study investigated the influence of pretreatment conditions of helium/oxygen (He/O2) atmospheric pressure plasma, including treatment duration, oxygen flow, and distance between the nozzle and the sample (DBNS), on sizing properties of cotton roving. Results indicate that plasma treatment can effectively improve the surface roughness, static friction coefficient, and the wettability of raw cotton fibers, as well as the absorption ability of cotton rovings for starch size. Consequently, sizing adhesion strength (SAS) and breaking elongation (BE) of the roving sized by starch are greatly influenced by the treatment. They first rise and then slightly drop with the increase of treatment duration or oxygen flow, but decrease with the elongation of the DBNS. Compared with a roving without plasma pretreatment, pretreated rovings can possess 59% and 36% improvement of SAS and BE, respectively, by a chosen plasma treatment condition, i.e. 15 s of treatment duration, 1.5 mm of DBNS, 30/0.3 L/min of He/O2, and 40 W of the power.