Nowadays, resin mortar (concrete) is widely used in various fields. The flowability of resin mortar in the uncured state is one of the important properties for its usage. The usual methods of measuring flow of fresh cement mortar (concrete), such as the flow test and the slump test, are, however, inapplicable on resin mortar because of adhesiveness of resin mortar.This paper describes a method of measuring resin mortar flowability using a rotational viscometer and the characteristic points of resin mortar flowability, obtained by this method. The rotational viscometer used was of a Couette type with the following dimensions;Inner cylinder: 120mmφ, 120mm height.Outer cylinder: 180mmφ, 200mm height.The results obtained are summarized as follows;(1) The present rotational viscometer is well suited for the study of resin mortar flowability. When compared with cement mortar having a similar appearance, resin mortar had higher viscosity but lower yield stress.(2) Super fine silica powder (7mμφ) increased the yield stress of resin mortar.(3) The amount of CaCO3 powder showed large influence on both the viscosity and compressive strength of resin mortar. The minimum value in viscosity and the maximum value in compressive strength were obtained at 25-35% of total aggregate.(4) From the temperature dependence of resin mortar viscosity, the activation energy of flow for resin mortar was found to be 7.1Kcal/mol, which is nearly equal to that of the resin (7.6Kcal/mol). This similarity in activation energy indicates that the viscosity of resin is a dominant factor in resin mortar viscosity.