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Ant-hemipteran mutualism has been well documented, and many studies have reported the interference competition between ant species for the mutualism. However, little is known on how this interference competition impacts the reciprocally beneficial association. Previous studies demonstrated that the invasive mealybug <i>Phenacoccus solenopsis</i> (Tinsley) has established close mutual relationship with the ghost ant <i>Tapinoma melanocephalum</i> (Fabricius). The sympatric ants, <i>Paratrechina longicornis</i> (Latreille) and <i>Tetramorium bicarinatum</i> (Nylander) were frequently observed to compete for nutrient honeydew produced by <i>P. solenopsis</i> with <i>T. melanocephalum</i>. Herein, we investigated the effects of interference competition between the ant species on the ant-mealybug interactions. <i>Phenacoccus solenopsis</i> benefited from the tending by <i>T. melanocephalum</i> and <i>P. longicornis</i>. Interference competition between <i>T. melanocephalum</i> and <i>P. longicornis</i> interrupted the mutualism, suppressed the trailing activity of both species, but negligibly influenced the parasitism of <i>Aenasius bambawalei</i> Hayat, a solitary endoparasitoid of <i>P. solenopsis</i>. <i>Harmonia axyridis</i>, a predator of <i>P. solenopsis</i>, showed a significant avoidance when encountering with <i>T. melanocephalum</i> or <i>P. longicornis</i>, but not <i>T. bicarinatum</i>. Ant workers showed higher aggressiveness and lower exploratory activity when <i>T. melanocephalum</i> encountered <i>P. longicornis</i>. However, competition between <i>T. melanocephalum</i> and <i>T. bicarinatum</i> seldom influenced the trailing and exploratory activity of <i>T. melanocephalum</i>. It is concluded that interference competition for mutualism between ant species can mediate ant-mealybug associations and the fitness of mealybug colony. Our results also demonstrate that the effects of interference competition between ant species on ant-mealybug mutualism are varied among ant species.