Background: Cataract is a leading cause of visual impairment and the senile cataract is the most common type. The role of Serum calcium to magnesium ratio (Ca-Mg ratio) in the pathogenesis of age-related or senile cataract remains unclear. Objectives: The objective of the present study is to estimate serum calcium, magnesium and their ratio levels in Senile cataract patients compared to normal healthy individual without cataract and to find out association of serum magnesium and calcium-magnesium ratio with risk of senile cataract. Subjects and methods: This case-control study consists of 90 Age-related cataracts (ARC) as cases and 90 age and gender matched normal healthy individuals without cataract as controls (age group above 45 years). The ARC patients were sub-grouped into nuclear cataract (NC), cortical cataract (CC), posterior sub-capsular cataract (PSC) and mixed cataract according to WHO cataract grading system. Serum calcium was determined by Arsenazo III method and serum magnesium by xylidyl blue method using Hitachi 902 autoanalyser. Results: The study shows significantly decreased concentration of serum magnesium and increased concentration of calcium-magnesium ratio (p<0.001) in ARC when compared to control. Pearson’s correlation analysis showed a significant negative correlation of serum magnesium with calcium was observed. Serum calcium-magnesium ratio was statistically identified as risk factors in ARC patients by using Multivariate logistic regression analysis (odds ratio, 5.177; 95% confidence interval, 0.483–2.805; p=0.006). Conclusion: Decreased serum magnesium concentration and increased serum calciummagnesium ratio were significantly associated with a high risk of cataract formation in patients with age-related cataract.