Background: The disabling nature of Parkinson’s disease (PD) impairs functional mobility and worsens quality of life. Calcium imbalances are thought to have a significant role in the progression of PD. Objective: To evaluate the relation between calcium deficiency and deterioration of PD motor symptoms. Methods: A total of 28 idiopathic PD patients were subjected to motor symptoms evaluation using the modified Hoehn–Yahr scale (H–Y), Unified Parkinson’s Disease Rating Scale (UPDRS) Part II and III and Schwab and England Activities of Daily Living Scale (S–E ADL). Total and ionized serum calcium levels were measured for the PD patients and the 30 healthy control subjects. Results: The level of ionized calcium was significantly lower among PD patients (4.19 mg/dl ± 0.53) than in control subjects (4.8 mg/dl ± 0.35) (p < 0.0001). The PD patients with hypocalcemia showed marked deterioration of motor symptoms and significant impairment of daily life activities when compared to PD patients with normal calcium levels regarding their scores on the modified H–Y scale (p = 0.001), UPDRS-III (p = 0.001), UPDRS-II (p = 0.001), and S–E ADL scale (p = 0.001). Ionized calcium correlated significantly with PD patients’ scores on the modified H–Y scale (p = 0.019), UPDRS-Part II (p = 0.001), UPDRS-Part III (p = 0.001) and S–E ADL scale (p = 0.001). The significant cutoff point of the ionized calcium for detection of the deteriorated PD patients that presented with stages more than grade 2 of the modified H–Y scale was < 3.99 (p = 0.037) with a sensitivity of 80% and specificity of 95%. Conclusions: Our findings conclude that calcium deficiency could contribute to the deterioration of PD motor symptoms. Keywords: Parkinson’s disease, Calcium, Motor symptoms