In the present study, the concentration ratio of the parabolic trough collector using rhombustube absorber has been estimated. An analytical technique has been developed to determine the optimum size of the rhombus tube absorber for given trough dimensions. The optimum size of the rhombus tube absorber is 13.8% smaller than the circular tube absorber for the LS3 trough with no change in intercept factor. The maximum improvement in the concentration ratio is found to be 31.5% for the troughs with rim angle 90 degrees in comparison to circular tube absorber. Results also indicate that rhombus tube absorber can be employed for a range of rim angle 75 to 90 degree.Abbreviations: CR: concentration ratio; CSP: concentrated solar power; MCRT: Monte Carlo ray tracing; PTC: parabolic trough collector