We present optical spectroscopy and extensive RI differential photometry of the double-lined eclipsing binary NSVS 02502726 (2MASS J08441103+5423473). Simultaneous solution of two-band light curves and radial velocities permits determination of precise empirical masses and radii for both components of the system. The analysis indicates that the primary and secondary components of NSVS 02502726 are in a circular orbit with 0.56-day orbital period and have stellar masses of M 1 ¼ 0:714 AE 0:019 M , and M 2 ¼ 0:347 AE 0:012 M . Both of the components have large radii, being R 1 ¼ 0:645 AE 0:006 R , and R 2 ¼ 0:501 AE 0:005 R . The principal parameters of the mass and radius of the component stars are found with an accuracy of 3% and 1%, respectively. The secondary component's radius is significantly larger than model predictions for its mass, similar to what is seen in almost all of the other well-studied low-mass stars which belong to double-lined eclipsing binaries. Strong H a emission cores and considerable distortion at out-of-eclipse light curve in both R and I bandpasses, presumably due to dark spots on both stars, have been taken as an evidence of strong stellar activity. The distance to system was calculated as 173 AE 8 pc from the BVRIJHK magnitudes. The absolute parameters of the components indicate that both components are close to the zero-age main-sequence. Comparison with current stellar evolution models gives an age of 126 AE 30 Myr, indicating the stars are in the final stages of pre-main-sequence contraction.