Two indigenous rangeland species, Cenchrus ciliaris L. and Coelachyrum piercei L.were investigated with Chloris gayana L. under Arabian Peninsula Research Program (APRP) of ICARDA (International Center for Agricultural Research in the Dry Areas) to know the effect of harvesting time on seed weight (husked) per se and quality from November 2002 to May 2004 spanning seven harvests in two different locations (Livestock Research Center (LRC), Rumais in the Batinah region and Agriculture Research Station (JRS), Jimah in the Interior region) of Oman. At each harvest, inflorescences were collected at physiological maturity (PM), one week after PM (1WAPM), two weeks after PM (2WAPM) and three weeks after PM (1WAPM). In all the grass species there was gradual and significant decrease (p<0.05) in seed weight/inflorescence from physiological maturity (PM) to subsequent harvesting times with significant increase (improvement) (p<0.05) in germination % from PM to 1WAPM or 2 WAPM and then decrease at 3WAPM. Interaction effect of harvests x harvesting times was highly significant (p<0.01) in all the grass species. At LRC and JRS, germination % was significantly higher (p<0.05) at 2WAPM (55.67 to 69 %) than that at preceding and succeeding times with significant loss of seed weight/ inflorescence (5 to >10%) during November and February when fairly cool temperature and low humidity exist. May or summer figures showed differential response of grass species in producing good quality seeds at LRC (hot and humid) and JRS (hot and dry). The results indicated that these grass species could be harvested within couple of weeks after physiological maturity for optimum high quality seed yield in Oman.