Knowledge management literature offers inconsistent findings on the moderating effects of employee's exchange ideology (EI) on the relationship between organizational instrumentality (e.g. reward) and employee's knowledge sharing behaviour (KS). This study contributes to the literature by examining how interaction effect of EI and instrumentality (INS) depends on the task environment variable-task visibility (TV). The results show that TV×EI×INS had a significant interaction in the prediction of employee's knowledge sharing behaviours in the organization. Specially, in the work environment of high task visibility, the positive relationship between INS and KS is stronger when the employee's EI is higher. In the environment of low task visibility, INS is unrelated to KS regardless of the level of individuals' EI. Theoretical and practical implications are discussed in the final section.