This paper presents the numerical study on the modal behaviour of skew-curve concrete box-girder bridges. 3-D finite element models for different curvature angles ranging between 0° to 90° at an interval of 30° with combination of skew angles of 0°, 15°, 30°, 45° and 60° have been developed in finite element program CSiBridge. Modal analysis for each bridge configuration is performed to generate mode shapes, time periods and modal mass participating ratios in the three orthogonal directions. With change in bridge configuration, variations of the time period and modal mass participation ratio is presented in graphical form for vertical and horizontal vibration modes. Results showed that time period of the first in-plane vibration mode is usually decreasing with increase in curvature as the in-plane bending flexibility of the deck decreases due to arching action which occurs because of increase in curvature. However, the time period increases with increase in skew angle for first in-plane vibration mode. Time period of first longitudinal mode is usually increasing with increase in skewness and curvature. Modal mass participation ratios are also found to increase with increase in skewness and curvature for first in-plane vibration mode. These ratios show complicated and variable behaviour in higher modes with high skew-curve combinations. These results hold pivotal role in determining the seismic response of skew-curve bridges.