National maize productivity is very low in Nepal. Increase of the productivity is only possible through growing high grain yielding single cross hybrid maize cultivar. So, development and evaluation of maize hybrids are principal steps to select high grain yielding and superior hybrid for cultivar. For it, fifteen newly bred single cross hybrids of yellow maize were examined from the standpoint of chlorophyll (chl) dynamics and their effects on grain yield. For it, a trial of RCBD experiment was conducted in open field in winter in subtropical region in Nepal. Seeds were sown on October 3, 2012 plot in two row plot area of 1.4 x 3.0 m2. After anthesis, chl and N concentration (conc) implying RAT (red light absorbance-transmittance) SPAD measure were taken from the topmost ear (e0) and third (e3) leaf above the e0 in ten days interval during grain filling. SPAD measures were transformed to total chl and N conc. E0 leaf has been found more grain yield determining than e3 leaf and terminal grain filling duration has been found more determining than early grain filling from the standpoint of correlation of grain yield with chl, N conc and SPAD measure. From pooled variance analysis; SPAD and chl conc were not significant different in different leaves and among the hybrids (Hybrids x Leaves x Ages). But, the SPAD and chl conc were significant different among the two leaves and ages (Leaves x Ages) irrespective of the hybrids. Different to the SPAD and chl conc, N conc was significant different in the leaves among the hybrids with respect to ages of the plants among the hybrids (Hybrids x Leaves x Ages). Thirteen top high grain yielding hybrids (HGYHs) 8, 12, 11, 13, 5, 6, 10, 1, 7, 14, 2, 9 and 15 were non-significant different from the standpoint of grain yield. The SPADs were in the non-significant range of 51-55 in e0 leaf in the duration from 95 to 125 d among the fifteen hybrids. Among the top four HGYHs 8, 12, 11 and 13; hybrid 11 lost chl and N from e0 leaf significantly on 135th d relative to the most of the hybrids. It means that the hybrid 11 could efficiently degrade N containing soluble protein and chl even from e0 leaf relatively. Top five HGYHS 8, 12, 11, 5 and 6 except 13 among the top listed ten hybrids constantly maintained chl and N conc implying SPAD in the e0 leaf up to the 135th d. In addition, it implies that these five hybrids sent newly up-taken N to kernels without degradation of the proteins and chl from the e0 leaf till the age of 135 d. HGYH 8 had degraded soluble proteins and enzymes and chl in e3 leaf and mobilized the degraded N to the kernels more efficiently from the e3 leaf. It is not necessary that maize hybrids must constantly maintain soluble proteins and chl conc during most of early to mid-grain filling duration for high grain yield. Instead, efficient reasonable decline of the soluble protein and chl conc during early to mid-grain filling also accelerate grain filling phenomena.