The disintegration of liquid by rotary cups has been investigated experimentally. The mechanism of direct drop formation and ligament formation in a rotary cup was studied using photos taken by a highspeed camera. Two kinds of liquids and three kinds of cups were used in the experiment. In the study, we found that three different types of disintegration formation occur as the angular speed increases in a given flow rate. The equations have been derived theoretically for calculating diameter of liquid drop produced by direct drop formation and ligament formation and the dimensionless equations obtained from the experimental results are applicable for calculating diameter of drops in a wide range of operating conditions. In the process of disintegration by ligament formation, the diameter of liquid drop is determined by the diameter of tail end of ligament, which was constant in diameter. The transition equations from direct drop formation to ligament formation and ligament formation to sheet formation arranged by three dimensionless parameters and compared with various experimental results. The transition equations fit quite well in the trend shown by the experimental date and they are applicable in a particular range of We, i.e. 10(3) < We <10(5). (C) 2012 Elsevier Ltd. All rights reserved.