Objective To evaluate the left atrial functions on diagnosis of paroxysmal atrial fibrillation (PAF) by real-time three dimensional echocardiography (RT-3DE). Methods Eighty-eight patients with [n = 45, 28 men, age (52.6 ± 11)] or without [n = 43, 27 men, age (50.8 ± 9)] PAF were studied. Parameters of left atrial size (LA size), E and A velocities and E/A ratio were obtained by two-dimensional echocardiography; and Ve and Va at the septum and lateral edge of the mitral annulus were recorded by tissue Doppler. The maximal left atrial volume (LAVmax), minimal left atrial volume (LAVmin), pre-atrial contraction left volume (LAVpreA), atrial reservoir volume (ARV) and active empty volume (AEV) were measured off-line by RT-3DE. Results Compared to normal controls, LA diameter, Ve, E/e, LAVmax, LAVpreA, and LAVmin significantly increased in patients with PAF; and ARV/LAVmax and AEV/LAVpreA significantly decreased (P < 0.05). Conclusions RT-3DE confirmed that LA reservoir function and booster pump function are impaired in patients with PAF.