Basilar artery is formed by the fusion of right and left vertebral artery and terminates as right and left posterior cerebral arteries. The aim of the study is to observe the diameter of basilar artery at three different levels (at its formation, at its midlevel and at its termination). This cross sectional descriptive study was performed on total 60 postmortem human hindbrain to find out the variation of position and diameter of the basilar artery of Bangladeshi people in relation to age. The specimens were collected from morgue in the department of Forensic Medicine, Mymensingh medical College, Mymensingh, Bangladesh by purposive sampling technique. All the specimens were grouped into four categories: Group A (20 to 29 years), Group B (30 to 39 years), Group C (40 to 49 years) and Group D (50 to 59 years). Diameter of basilar artery was measured with the help of digital slide calipers at three different levels. At the level of its formation, mean±SD diameter was 3.76±0.37 mm, 3.75±0.32 mm, 3.68±0.24 mm & 3.54±0.46 mm in Group A, B, C & D respectively. At mid-level, it was 3.49±0.36 mm, 3.48±0.30 mm, 3.45±0.21 mm & 3.36±0.44 mm in Group A, B, C & D respectively. At the termination, it was 3.55±0.35 mm, 3.51±0.30 mm, 3.48±0.22 mm & 3.38±0.38 mm in Group A, B, C & D respectively. This knowledge of variations of the diameter of basilar artery is of diagnostic importance for the neurosurgeons and radiologists for clinical investigation and surgery.