Purpose - Justice, although well developed in the organisational field, has not been given adequate attention in the area of construction project dispute negotiations. Based on previous studies, the purpose of this paper is to more elaborately discuss whether each dimension of justice (distributive, procedural and interactional) is important for negotiators to cooperate in construction project dispute negotiation and whether their impact was moderated by the completeness of construction contract. Design/methodology/approach - A survey of 164 prime negotiators from different construction projects was conducted. A stepwise multiple regression was employed to test the impact of each dimension of justice, and then a moderated multiple regression model was used to test the moderating effect of contract completeness. Findings - The results indicated that, while distributive justice is related to cooperative behaviours, the impact of procedural justice and interactional justice also have great impact, and even more significantly related to cooperative behaviours. Moreover, while contractual obligatoriness positively moderates the relationship between procedural justice and cooperative behaviours, the term specificity negatively moderates the relationship between procedural and interactional justice and cooperative behaviours. Research limitations/implications - First, the authors aimed to test the effect of justice on cooperative behaviours in construction dispute negotiations originally, but did not determine whether their relationship is mediated by any other factors. Second, contractual governance was chosen as the moderator; other factors may also influence behaviours in project dispute negotiations. Practical implications - First, project dispute negotiators should not focus their attention solely on the distribution of the negotiation issues. For a cooperative approach, negotiators should also give strong consideration to whether their offers reflect procedural justice and whether their opponents are being treated fairly. Second, while contractual design may affect the frame surrounding the negotiations to help negotiators achieve an integrated outcome, they should give more attention to certain forms of justice. Originality/value - In contrast to previous studies, the authors defined all three forms of justice in project dispute negotiations, and by adding all three forms of justice into the model, the authors attempted to investigate whether distributive, procedural and interactional justice were all related to cooperative behaviours in project dispute negotiations and to ascertain the extent to which each form of justice is important. Furthermore, the authors explored variations in the importance of each form of justice in negotiations under different contractual conditions.