The current study investigated infants' spontaneous object interactions during naturalistic observation in a daycare centre in Japan. The researcher visited the class for 49 days, once a week, for one year (in the morning for about 1.5 h). Infants' and caregivers' interactions during free play time were videotaped. Of particular interest in this study was whether changes in infants' locomotor status were functionally related to social exchanges with objects. During longitudinal one-year observation, all six infants gradually acquired locomotor skills: two infants became walkers from pre-crawlers, and another four became walkers from crawlers. Throughout the observations, the infants spent an impressive amount of time (i.e. about 50%) in contact with objects. As they acquired locomotor skills, they gained access to distal objects and carried objects frequently. Triggered by the onset of walking, infants' carrying behaviour increased dramatically. Locomotor experiences were also related to qualitative changes in how they used objects in social interactions. These quantitative and qualitative changes in infants' object experiences were not strongly connected with the infants' age in months. Taken together, this study demonstrated that the onset of walking marks a critical developmental milestone that profoundly changes the way infants access, carry, and use objects to interact with others.