In this study, we demonstrated a single-layer silicon nitride (SiNx) film deposited on polyethyleneterephthalate substrate as a moisture permeation barrier film that reduced the water vapor transmission rate (WVTR). The SiNx film was fabricated by roll-to-roll, plasma-enhanced chemical vapor deposition (R2R-PECVD) in widths as large as 500 mm. The effects of the NH3/SiH4 flow ratio on the SiNx properties were investigated according to their refractive index, optical characteristics, film density, WVTR, and chemical composition. The durability of the flexibility of the SiNx film was investigated via outer/inner bending test and cyclic bending fatigue test. The SiNx film showed excellent thickness uniformity and optical properties. M the NH3/SiH4 flow ratio of 3, the SiNx film exhibited the highest film density and the best moisture barrier performances of 1.67 x 10(-3) g/m(2).day. The results of the inner bending test showed that the flexibility of the SiNx film was excellent. The test results showed that the failure bending radius was 2 mm. The durable flexibility of the SiNx film was influenced by the internal residual stress and microstructure. After 10,000 cyclic inner-bending fatigue tests, no crack was observed, and the WVTR values were maintained below 2.0 x 10(-3) g/m(2).day. These results indicate that the single-layer SiNx film fabricated with a simple R2R PECVD has a high potential as a moisture barrier film for future flexible electronic applications.