While dialectical behaviour therapy (DBT) appears efficacious in reducing suicidal and self-harming behaviour, it is unclear whether DBT reduces emotion regulation (ER) difficulties, a purported mechanism of change of treatment. This review aims to investigate and evaluate the current evidence to understand the effectiveness of DBT in improving ER difficulties. A qualitative synthesis of studies investigating the effectiveness of DBT on self-reported ER difficulties as measured by the Difficulties in Emotion Regulation Scale (DERS) was performed, identifying eligible studies using PsycINFO, PubMed, MEDLINE and EMBASE databases. Fourteen studies were identified. Current evidence indicates that DBT does not show consistent benefits relative to existing psychological treatments in improving ER difficulties. The literature is compromised by significant methodological limitations increasing risk of bias across study outcomes. Furthermore, high variability across DBT programs and a lack of investigation regarding adherence and participant engagement within interventions was observed. Further research is needed in order to conclude regarding the effectiveness of DBT in improving ER difficulties. Consistent use of active treatment conditions, greater standardisation of DBT-based interventions, in addition to further examination of participant engagement level in DBT-based interventions in the long term may assist understanding as to whether DBT improves ER difficulties.