Abstract: Objective: To examine the bidirectional longitudinal associations among internet use, social isolation, and loneliness in Chinese middle-aged and older adults, and to explore potential gender differences in these relationships. Methods: Using two-wave follow-up data (2018 and 2020) from the China health and retirement longitudinal study (CHARLS), a cross-lagged panel model was established to analyze the autoregressive and cross-lagged effects among internet use, social isolation, and loneliness. Gender-stratified analyses were further performed. Results: Autoregressive analyses indicated temporal stability in internet use, social isolation, and loneliness among middle-aged and older adults over time (P＜0.001). Cross-lagged analyses revealed a bidirectional negative predictive relationship between internet use (β=-0.185, 95% CI: -0.213 to -0.156) and social isolation (β=-0.319, 95% CI: -0.366 to -0.272). Social isolation positively predicted later loneliness (β=0.091, 95% CI: 0.056 to 0.126), whereas loneliness reduced subsequent social isolation (β=-0.056, 95% CI: -0.094 to -0.018). Loneliness positively predicted later internet use (β=0.139, 95% CI: 0.090 to 0.188), while internet use decreased subsequent loneliness (β=-0.053, 95% CI: -0.081 to -0.024). The autoregressive and cross-lagged patterns in males were largely consistent with the overall results. However, among females, the predictive effects of internet use on loneliness and of loneliness on social isolation did not reach statistical significance. Conclusion: Internet use, social isolation, and loneliness are reciprocally associated among Chinese middle-aged and older adults. Accordingly, encouraging internet use among community-dwelling middle-aged and older adults is warranted to enhance social connectedness, reduce loneliness, and promote mental health.