This initial open feasibility trial reports on feasibility and preliminary effectiveness of the manualized, group-based psychoeducational intervention for grandparents of preschool-aged children with ASD provided by the outpatient habilitation services in Stockholm, Sweden. One hundred and twenty non-custodial grandparents participated in a 6-h intervention program. The study demonstrated good feasibility: 114 (95%) grandparents completed both pre- and post-intervention measures and evaluations and reported high intervention acceptability. The results also indicated that grandparents increased their knowledge about ASD from pre-intervention to post-intervention, gained skills about strategies of supporting their grandchildren and adult children, and appreciated the opportunity to meet and share experiences with other grandparents. Follow-up with a randomized controlled trial design is needed to firmly establish efficacy of this intervention.