Novel, high-strength, microfibrillar poly(vinyl alcohol) fibres (PVA fibrils) having a number-average degree of polymerization (P-n) of 4500-20 000, a degree of saponification (DS) of 85.0-99.9% and a syndiotactic dyad (S-dyad) content of 57-64% could be prepared successfully by saponifying under shearing force poly(vinyl pivalate) having a P-n of 11 300-33 000. The saponifying agent used was a mixture of potassium hydroxide, water and methanol. The PVA fibrils had dimensions of 1-50 mu m in diameter, 0.5-200 mm in length, irregular cross-sections and needle-point-like ends. The high-strength PVA fibrils prepared by the fibrillation method had an orientation index of over 0.88, a crystallinity of over 48%, a crystal melting temperature of higher than 260 degrees C and an accumulated ultrafine microfibril structure. The PVA fibrils having a P-n of over 10 000 exhibited higher than 12 g den(-1) of maximum tensile strength and their resistance to hot water was excellent. Moreover, these properties were enhanced by increases in the P-n, S-dyad content and DS of the PVA fibrils.