The objective of this study was to determine the mediating role of loneliness in the relationship between internet aggression and internet addiction with marital conflicts among couples in Rasht. The present study was descriptive–correlational in nature. The statistical population consisted of couples referring to family counseling offices and the family court in Rasht. The research sample included 100 couples (200 individuals) who were selected through purposive sampling from among those willing to participate in the study; the sample size was considered sufficient based on the criteria for structural equation modeling. Data collection instruments included: a demographic questionnaire, the Marital Conflict Questionnaire (Barati & Sanai, 2000), the Social and Emotional Loneliness Scale for Adults (SELSA-S), Young's Internet Addiction Questionnaire (1988), and the Internet Aggression Questionnaire (Shajari-Toobi, Atashpour, & Golparvar, 2016). Data analysis was performed using structural equation modeling with the partial least squares (PLS) approach in SPSS and PLS version 3 software. The results of the mediation test showed that loneliness played a significant mediating role in the relationship between internet addiction and marital conflicts, as well as in the relationship between internet aggression and marital conflicts. Accordingly, it can be concluded that loneliness, as an important psychological mechanism, explains the relationship between cyberspace-related harms (internet addiction and internet aggression) and marital conflicts.