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We obtained thorough photometric observations of two binary near-Earthasteroids (66391) Moshup = 1999 KW4 and (88710) 2001 SL9 taken from 2000 to2019 and derived physical and dynamical properties of the binary systems. Wefound that the data for 1999 KW4 are inconsistent with a constant orbitalperiod and we obtained unique solution with a quadratic drift of the meananomaly of the satellite of -0.65 +/- 0.16 deg/yr2 (all quoted uncertaintiesare 3sigma). This means that the semimajor axis of the mutual orbit of thecomponents of this binary system increases in time with a mean rate of 1.2 +/-0.3 cm/yr.  The data for 2001 SL9 are also inconsistent with a constant orbital periodand we obtained two solutions for the quadratic drift of the mean anomaly: 2.8+/- 0.2 and 5.2 +/- 0.2 deg/yr2, implying that the semimajor axis of the mutualorbit of the components decreases in time with a mean rate of -2.8 +/- 0.2 or-5.1 +/- 0.2 cm/yr for the two solutions, respectively.  The expanding orbit of 1999 KW4 may be explained by mutual tides interplayingwith binary YORP (BYORP) effect (McMahon and Scheeres, 2010). However, amodeling of the BYORP drift using radar-derived shapes of the binary componentspredicted a much higher value of the orbital drift than the observed one. Itsuggests that either the radar-derived shape model of the secondary isinadequate for computing the BYORP effect, or the present theory of BYORPoverestimates it. It is possible that the BYORP coefficient has instead anopposite sign than predicted; in that case, the system may be moving into anequilibrium between the BYORP and the tides.  In the case of 2001 SL9, the BYORP effect is the only known physicalmechanism that can cause the inward drift of its mutual orbit.

A satellite orbit drift in binary near-Earth asteroids (66391) 1999 KW4 and (88710) 2001 SL9 -- Indication of the BYORP effect