The aim of the present study was to determine the effect of proprioceptive neuromuscular facilitation (PNF) leg patterns on the muscle activation of neck flexors. Twenty healthy subjects participated in this study. Each subject performed bilateral asymmetrical PNF leg patterns against manual resistance under four conditions: through the full range of motion toward the right side, left side, and the end range in the right side, left side. Electromyographic (EMG) data was collected from the sternocleidomastoid (SCM) muscles as neck flexors. The root mean square (RMS) value of the SCM was measured and normalized from maximal EMG activity of the SCM. The data were analyzed using the paired t-test and repeated analysis of variance (ANOV A) was used to compare the statistical significance. The results of this study are summarized as follows: Firstly, the RMS values of SCM were significantly higher in all four PNF leg patterns than in the resting condition (p<.05). Secondly, there was no significant difference in muscle activation according to the direction of PNF leg patterns (p>.05). Thirdly, there was no significant difference in muscle activation according to the point of range of the motion of leg patterns (p>.05). It is suggested that PNF bilateral asymmetrical leg patterns have a considerable effect on muscle activation of the SCM, regardless of the range of motion and direction of PNF bilateral asymmetrical leg patterns.