While no exact information on the prevalence exists, it is assumed that the overall incidence of children with autism spectrum disorder (ASD) has risen every year in Japan. However, given the lack of resources and services for families of children with ASD in Japan, there is a dearth of practical guidance for the support for those families. This study examined the effects of an asynchronous training package (i.e., self-paced and video-based learning manual) to teach two Japanese mothers to implement incidental teaching. Effectiveness of the instruction was determined using a multiple-baseline design across mother-child dyads. Results indicated that the mother participants were able to implement the intervention with high fidelity over time. However, mixed effects of the mother-delivered intervention on target language behaviours were found across the child participants' behaviours. This study adds an evidence to support that parents can be essential and efficient intervention agents for children with ASD.