The relationship between temporal bone pneumatization and position of sigmoid sinus, length of mastoid process were investigated by plain X-ray(Law's view) in 134 healthy ears and 113 ears suffered from chronic otitis media or cholesteatoma. And additionally air-cell type and mastoid tip pneumatization were investigated. Position of sigmoid sinus and posterior EAC wall and between superior petrosal ridge and mastoid tip. Type of mastoid air-cell was classified as small, moderate, and large. Tip cell pneumatization was classified as pneumatic, diploic, and sclerotic. Measurement of pneumatized areas were performed by computer coordinating area curvimeter. Statistic analysis was performed by SPSS/PC⁺ and SigmaPlot program. The following results were obtained ; 1) Mean area of mastoid pneumatization was 1512.61mm²(SD 452.35mm²) in normal group, 767.54mm²(SD 193.52mm²) in COM group. Difference between two groups had a statistic significance(p<0.0001). 2) Mean length of mastoid process was 38.82mm(SD 4.79mm) in normal group, 35.20mm(SD 5.47mm) in COM group. Difference between two groups had a statistic significance(p<0.001). 3) Mean distance between posterior EAC wall and sigmoid sinus were 15.03mm(SD 2.89mm) in normal group, 13.01mm(SD 2.51mm) in COM group. Difference between two groups had a statistical significance(p<0.0001). 4) The length of mastoid process was shorter in cases with small pneumatization as well as the distance between posterior EAC and sigmoid sinus(r=0.28, p<0.001 ; r=0.41, p<0.001). 5) Relationship between length of mastoid and position of sigmoid sinus had a positive correlation(r=0.32, p<0.001).