Objectives: Hoarding in older adults can have a detrimental effect on daily life. Repetitive negative thinking (RNT) could result in a greater avoidance of discarding and increased saving behaviors; yet, the unique role of RNT on hoarding in older adults remains understudied. This study aimed to investigate whether the intensity of RNT contributes to hoarding in older adults. Methods: Two hundred and sixty-four older adults in Japan (ages 65–86 years, 132 males and 132 females) participated in an online survey. Hierarchical regression analyses were conducted to examine whether RNT could significantly explain the variance of hoarding after controlling for age, sex, years of education, self-reported cognitive impairment, and depression. Results: As we expected, RNT was significantly associated with greater hoarding behaviors, such as excessive acquisition (β = .27, p = .005) and difficulty in discarding (β = .27, p = .003). On the other hand, reflection, repetitive thinking without negative emotional valence, was significantly associated with higher scores on clutter (β = .36 p < .001). Conclusion: Our findings highlight the importance of addressing RNT in the prevention and treatment of hoarding symptoms among older adults, potentially leading to more effective interventions and improved outcomes in managing hoarding behaviors in this population.