Characteristics of dielectric filters based on multi-conductor transmission-line are analyzed. Assuming only TEM mode propagation, transmission-line characteristics are determined from capacitance matrices with and without dielectric materials inside the transmission-line. These capacitance matrices are calculated by cross-sectional analysis with Boundary Element Method. Frequency response of the filter is further modified by putting conducting patterns on the cross-section, of which circuit parameters are calculated by 3-dimensional Finite Element Method with quasi-static approximation. Calculated frequency responses show good agreements with experimental results.