Understanding the role of impurities in the process of crystal growth is not only of long-standing fundamental interest but is also important for controlling the morphologies and properties of micro/nanocrystals. In this paper, large quantities of single crystal AlN triangular microfibers were synthesized by physical vapor transport (PVT) method with the presence of Ni. We found that AlN triangular microfibers were evolved from hexagonal microfibers with the increase in growth time and Ni plays an important role in the process of evolvement. Then, the effect of Ni on the growth kinetics of AlN triangular microfibers was also investigated. Our results show that the relative radial growth rates of AlN (R/R(0)) mostly reduce with the increase of mole ratio of Ni to AlN powders (C(i)). The relation between R/R(0) and C(i) can be well fitted by competitive adsorption model (CAM). Three new red photoluminescence bands centered at about 600, 650 and 690 nm were observed in AlN triangular microfibers. At last, three important roles of Ni in the growth of single crystal AlN microfibers could be summarized, which provide useful information for controlling the morphology, size and property of AlN nano/micro-structures. (C) 2010 Elsevier B.V. All rights reserved.