Cognitive Stimulation Therapy (CST) is widely used with people with dementia, but there is no evidence of its efficacy in mild cognitive impairment or dementia in Parkinson’s disease (PD-MCI; PDD) or dementia with Lewy bodies (DLB). We aimed to explore the impact of ‘CST-PD’, which is home-based, individualised CST adapted for this population. In a single-blind randomised controlled exploratory pilot trial (RCT), we randomised 76 participant-dyads (PD-MCI (n=15), PDD (n=40), DLB (n=21) and their care partners) to CST-PD or treatment-as-usual (TAU). CST-PD involves home-based cognitively stimulating and engaging activities delivered by a trained care partner. Exploratory outcomes at 12 weeks included cognition (Addenbrooke’s Cognitive Evaluation; ACE-III), neuropsychiatric symptoms and function. In care partners, we assessed burden, stress and general health status. Relationship quality and quality of life were assessed in both dyad members. At 12 weeks, the ACE-III showed a non-statistically significant improvement in the CST-PD group compared to the TAU group, although neuropsychiatric symptoms increased significantly in the former. In contrast, care partners’ quality of life (d = 0.16) and relationship quality (‘satisfaction’, d=0.01; ‘positive interaction’, d = 0.55) improved significantly in the CST-PD group, and care burden (d = 0.16) and stress (d = 0.05) were significantly lower. Qualitative findings in the CST-PD recipients revealed positive ‘in the moment’ responses to the intervention, supporting the quantitative results. In conclusion, care partner-delivered CST-PD may improve a range of care partner outcomes, which are important in supporting home-based care. A full-scale follow-up RCT to evaluate clinical and cost-effectiveness is warranted.