Populus deltoides G-3, a perennial fast-growing plant, indigenous to some western countries, can be grown ira the eco-climatic conditions of Assam, in particular and the north-eastern region of India, in general. The biomass obtained from plants of different age groups was exploited to prepare pulp and paper with characteristic physico-chemical properties. The age or maturity of a plant influences the mechanical properties of the fibres and, hence, the properties of the paper This investigation was carried out to study the degree of polymerization (DP), viscosity and fibrillation properties of pulps prepared under identical conditions from Populus deltoides wood of 2, 4, 6 and 8 years of age. It showed that the physical strength properties of paper sheets prepared from such pulps varied with the maturity of the plant The crystallinity (%) and crystallite sizes of the fibres were determined using X-ray diffraction and IR spectrometry. Pulp cellulose obtained from a 6-year-old plant showed high DP (1025) and viscosity (22.40 Cp) values, and the paper sheets from such pulp exhibited physical strength properties of burst index (7.3 kPa m(2) g(-1)), tear index (8.9 mN m(2) g(-1)) and tensile index (70.7 N mg(-1)). The crystallinity was found to be 45.1%, in pulp cellulose of 6-year-old wood, while crystallite sizes were 6.2 and 16.2 in (002) and (040) planes, respectively. All the above values were higher than those obtained from pulp fibres of 2-, 4- and 8-years-old wood Therefore, in a cultivation programme of Populus deltoides plants, harvesting is recommended after 6 years, to produce quality pulp for papermaking. Copyright (C) 1996 Elsevier Science Ltd.