The scale of professional sports leagues and mega sports events has expanded recently. Many sports fans travel to foreign countries to watch international events featuring the world’s top athletes or players. The number of international sports fan tourists has increased, and understanding their behaviour is very important for stakeholders and those involved in marketing, such as sports organisations, travel companies, and government tourist organisations. This study examines the motivations and constraints of Japanese international sports fan tourists and Japanese Rugby World Cup fan tourists. Sports fan tourists are tourists as well as sports fans. Many researchers have examined motivation either from a sports fan’s perspective or a tourist perspective. However, a motivation scale for international sports fan tourists (combining both sports fan and tourist motivations) has been not developed as there has been a lack of research into the behaviour of the international sports fan tourist. The main research aim of this study is to analyse the motivation and constraint factors of both Japanese international sports fan tourists and Japanese Rugby World Cup tourists. The methodology aims to: 1.profile Japanese international sports fan tourists and Japanese Rugby World Cup tourists; 2.develop a motivational scale for actual sports fan tourists and a constraints scale for potential sports fan tourists (those who considered going but did not go); 3.analyse these factors according to demographics; 4.examine factors related to motivations and constraints on fans’ satisfaction, or their intention to attend future events. A quantitative approach was employed. The main data collection methods were three email surveys: 1.Study 1 collected data about actual international sports fan tourists (N=338) and potential sports fan tourists (N=292). 2.Study 2 collected data about actual Rugby World Cup 1987-2007 tourists (N=101) and potential tourists (N=297). 3.Study 3 collected data about actual Rugby World Cup 2011 tourists (N=84) and potential tourists (N=115). In previous studies, the sample was collected either from actual fans or potential fans separately; however, in this study, samples were collected not only from actual sports fan tourists but also from potential sports fan tourists from the same database. The data analysis predominantly used explanatory factor analysis (EFA), confirmatory factor analysis (CFA), independent t-test, ANOVA, regression analysis, and structure equation modelling (SEM) including interaction effects analysis. The results of this study were analysed using four steps: 1.Showing the demographic profiles and behavioural patterns of Japanese international sports fan tourists and Japanese Rugby World Cup fan tourists. 2.Developing motivation and constraints scales: • an International Sports Fan Motivation Scale • an International Sports Fan Tourist Motivation Scale • an International Sports Fan Constraints Scale • a Rugby World Cup Sports Fan Motivation Scale • a Rugby World Cup Fan Tourist Motivation Scale • a Rugby World Cup Fan Constraints Scale. 3.Comparing the mean scores of extracted factors by demographics such as gender, age, sports experiences etc. 4.Analysing the impact on satisfaction or future intention using interaction effect methods. The results showed some interesting academic and practical implications. This study has thus made a significant and unique contribution to the knowledge of international sports fan behaviour by researching the combined sports fan motivation factors and tourist motivation factors of actual sports fans, and the constraints of potential sports fan tourists. The study has also provided an academic contribution to the sports and tourism fields, and has provided a practical contribution to the areas of sports fan behaviour, tourism, leisure constraints, and sports events management.