Bladder dysfunction is a common phenomenon in Parkinson's disease (PD) patients. A research attempt was made to analyze the voiding efficiency (VE) and bladder functions in rats with PD induced by unilateral or bilateral injections of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle. PD rats were divided into unilateral- and bilateral-injected groups and subjected to rotation and beam walking tests. Further, the experimental rats underwent cystometric measurements for analyses of bladder dysfunction and VE. Immunohistochemical analysis was performed to analyze the dopaminergic neuron depletion on the target area. Outcomes of the rotation and beam walking tests revealed the extent of parkinsonism in the experimental rats. Urodynamic observations denoted that rats with unilateral PD exhibited a significantly decreased VE (from 68.3±3.5% to 32.7±5.8%), while rats with bilateral PD displayed a much-reduced and substantially lower level of VE of 18.3±5.1% compared to the control value and to that of rats with unilateral PD. Rats with bilateral PD showed more-extensive behavioral deficits and urodynamic changes than did rats with unilateral PD. These significant changes in motor, behavioral, bladder function and VE were due to an extensive degeneration of dopaminergic neurons in the substantia nigra region on both sides of the brain. The obtained results were substantiated with appropriate immunohistochemical results.