Allosuckling has been reported in many mammalian species. In giraffe, allosuckling has been observed in captivity, and the milk theft hypothesis with reciprocity is regarded as the likeliest explanation for this behavior. However, reports of such behavior in the wild remain sparse to non-existent. Here, we studied the suckling and allosuckling behaviors of three nursing giraffe and their offspring (two calves and one juvenile) for 32 days in the Katavi National Park, Tanzania. In total, we observed 56 suckling bouts, 96 suckling attempts, 5 allosuckling bouts, and 71 allosuckling attempts. We observed that the female decided when to nurse the offspring, as reported in previous studies; however, the suckling bouts of calves were terminated mainly by other individuals. On the other hand, all suckling bouts of juvenile were terminated by the female. The milk theft hypothesis was supported since (1) the allosuckler always joined a suckling pair and never succeeded when approaching a female by itself, (2) the female apparently did not notice the non-filial offspring positioned behind the filial offspring, and (3) the female showed active signs of rejection when she noticed the allosuckler. In addition, we found that juvenile close to weaning showed the highest rate of allosuckling interactions. Therefore, we assume that the presence of a weaning individual might drive the occurrence of allosuckling in giraffe in the wild.