A higher proportion of patients with juvenile-onset systemic lupus erythematosus (JSLE) will have renal involvement compared with adult-onset disease, some progressing to renal failure in adulthood. Histological examination is the gold standard for diagnosing lupus nephritis (LN), but its invasive nature limits routine use. Using cross-sectional cohort analysis, we aimed to determine whether urinary concentrations of monocyte chemoattractant protein-1 (MCP1), alpha-1-acid glycoprotein (AGP) and interferon-inducible protein 10 (IP10) are biomarkers of active LN. Sixty JSLE patients recruited to the UK JSLE Cohort Study were categorized according to the British Isles Lupus Assessment Group (BILAG) activity index. Patients with active renal JSLE (n = 8; renal BILAG score A, B) had significantly higher urinary MCP1 concentrations than patients with inactive renal disease (n = 52; renal BILAG score C, D, E; 582 pg/mg creatinine [Cr], 207 pg/mg Cr; p = 0.018) or healthy controls (n = 23; 117 pg/mg Cr; p = 0.005). Urinary AGP concentration was significantly elevated in patients with active renal disease compared with inactive renal disease (1517 ng/mg Cr, 485 ng/mg Cr; p = 0.027) or healthy controls (313 ng/mg Cr; p = 0.013). Urinary IP10 concentration was not significantly different between groups, but did strongly correlate with uMCP and uAGP levels (rho = 0.38, p = 0.009; rho = 0.33, p = 0.021). Urinary MCP1 and AGP are biomarkers of LN, providing insight into its pathophysiology. Longitudinal studies are warranted.