Study on the Period Changes of xy Leonis

XY Leo (BD+18° 2307, p = 0d .28) was observed each season from 1992 through 1995 at Yunnan Observatory with the 1 m telescope and 37 new heliocentric times of minimum light were determined. The newly expanded database of the minimum times,including these new epochs, definitely confirm the sine-like variation of its O–C values. Observations and analyses strongly supported the viewpoint that the variation of the O–C values of the minimum times is mainly caused by the light- time effect. Based on this newly expanded database, new light elements for the eclipsing system XY Leo and new light-time orbit for this complex system have been obtained with much better accuracy than before by means of the least squares fitting to the light-time equation. It's also noted that the additional period variation for XY Leo probably may not be ruled out besides the light-time effect. The method of analysis and the discussion of the results are presented in this paper. This revised version was published online in July 2006 with corrections to the Cover Date.