Abstract: From the perspectives of developmental genetics and molecular ecology, this study reviewed the current state and issues of local and international rice grain-filling research. The authors contended that rice grain development was a complicated molecular ecological process, involving signal transductions, multi-gene regulations and environmental interactions. Different gene expressions in space and time, coupled with the action modes of functional proteins in superior and inferior grains caused significant differences in developmental programs of endosperm cells, grain-filling rates and dry matter accumulation at different spikelet positions on the panicle. Previous studies showed that superior grains were usually filled earlier and faster, leading to a significant genetic stability. The reverse was true for inferior grains, where stagnant and poor properties were associated with seed development and grain filling. It was noted that genetic characters were easily regulated by environmental factors during inferior rice grain-filling. Molecular genetic manipulations and molecular ecological regulations were two effective ways of improving inferior grain endosperm cell development, timely initiation of inferior grain filling, high percent setting and 1000-grain weight, and high yield. It was therefore emphasized to deeply understand the underlying mechanisms and properties of genetic ecology in grain filling (and especially in inferior grain-filling processes). This had become a priority grain production research area across the globe. Based on current understandings, it was suggested to focus further studies on investigating and answering the critical scientific questions of why there existed a stagnant phase in inferior grain filling and how different were protein expressions and associated functions of relevant genes between superior and inferior grains during the period of grain-filling.