Background Self-determination is regarded as an adult outcome for people with intellectual disability (ID). Students with ID in western countries learn self-determination knowledge and skills through the systematic curriculum in schools. However, the curriculum for adults with ID is still underdeveloped in the West. In Hong Kong, the self-determination curriculum is rarely available in any setting.

Objective The proposed study aims to develop a culturally-tailored self-determination enhancement group intervention for adults with ID and to evaluate its effectiveness.

Method The proposed study will consist of two phases. Phase one will develop the protocol for the self-determination enhancement intervention and establish its implementation fidelity through a panel review and pilot study. This phase will last eight months. Phase two will adopt a randomised controlled trial with pre-test, post-test and three-month follow-up. A total of 120 participants will be randomly assigned to three conditions: Self-determination enhancement group, Self-determination enhancement PLUS group (+ parents' involvement) and leisure activity group as a control condition. Five groups will be organised for each of the three conditions over 18 months. There will be 10 sessions per group covering the self-determination core components such as self-understanding, goal-setting and attaining, self-regulating and plan adjusting. Components for parents include understanding self-determination and skills in supporting people with ID to exercise self-determination through positive interaction. Validated instruments in Chinese will be filled in by participants. Statistical analyses will be conducted to examine if the effectiveness of this group intervention can be found and sustained over a three-month period, and the magnitude of change in self-determination competencies and quality of life.

Implications The proposed study is the first evidence-based local study aimed at examining a culturally-tailored self-determination enhancement intervention for people with ID. If the intervention demonstrated as effective, it will be used or modified for use with Chinese-speaking people with ID in different parts of the world.

Inclusion Criteria:

• Chinese people who have mild intellectual disability (i.e., assessed in their most recent psychological report)
• Aged 18 or above
• Able to master basic comprehension and verbal communication skills
• Willing to complete the group intervention.

Exclusion Criteria:

• Those who demonstrate severe challenging behaviours will be excluded