The potential of plant fibres in structural materials components is explored by applying textile hemp yarn for fabrication of composites with aligned fibres. This first paper presents a detailed characterisation of the hemp yarn. It is shown that the hemp yarn has a high cellulose content (about 90%), the fibres are evenly dispersed within the yarn with a mean twisting angle of about 11°, the moisture sorption capacity is relatively low (e.g. moisture content of about 8% at 65% RH), and the mechanical properties are good (e.g. tensile ultimate stress of about 660 MPa). These findings show that textile hemp yarn is well suited for composite reinforcement. The accompanying second paper is addressing the mechanical properties of the composites.