<p>Early adolescence represents a developmental period marked by increased vulnerability to loneliness and meaninglessness. Although theoretical frameworks posit reciprocal associations between loneliness and life meaning, longitudinal research examining their developmental trends and reciprocal associations has been limited. A total of 3825 Chinese junior high school students (47.5% girls; <i>M</i>_<i>age</i> = 12.36, <i>SD</i> = 0.50) participated in this five-wave longitudinal study, among whom 39.9% were only children and 80.7% came from middle-class families, with other demographic details presented later. The results showed that loneliness increased slowly in the first semester of seventh grade, rose sharply in the next semester, and grew steadily in eighth grade. Adolescents’ presence of meaning dropped sharply in the seventh-grade second semester, with slow declines continuing afterward. Parallel process latent growth modeling indicated that a faster increase in loneliness was associated with a greater decline in the presence of meaning. And random intercept cross-lagged modeling revealed that higher loneliness predicted lower subsequent the presence of meaning, whereas stronger the presence of meaning predicted reduced later loneliness, indicating co-development and bidirectional links in early adolescence.</p>