Nestling behavior and nestling growth of Yellow-bellied Prinia (Prinia flaviventris) were observed in Zhaoqing, Guangdong, China, from March to September, 2007. In this study, we recorded the food consume, nestling food composition and nestling measurements of Yellow-bellied Prinia to investigate its parental investment and nestling development pattern. The feeding behavior was observed through the window of hidden tent in a distance within 5 m from the nest. Nestlings were marked with colored, odorless pen on their backs when younger than 10 days old, and on their tarsus when nestlings were 10, 11 and 12 days old. Bivariate correlation was employed to analyze the relationship between nestling age and types of food fed by their parents, and the correlation matrix of nestling measurements. Also, logistic growth curve was used to fit the nestling growth data, and the k value of each regression was performed a significance test. Our results showed that: 1) Nestlings were fed by both parents, with the nestling period of 11.9 ± 0.4 d (n = 7). When nestlings were less than 7 days old, parents spent more time on warming nestlings in the morning and evening; 2) Feeding frequency and the types of food increased as nestlings grew older, with nestling age positively correlated with parental feeding frequency (r = 0.995, P < 0.01); 3) Nestlings were fed with arthropods only, with the spiders being the most (40.95%) and others including larvas, Orthoptera, Lepidoptera, Coleoptera, Odonata and so on (Fig. 1); 4) The k value of growth curve for body weight (Fig. 2) was the maximum value (Table 1), and differed significantly from other k values (P < 0.05) of length growth curves (Fig. 3); 5) All the correlation coefficients among body measurements (body weight, body length, tail length, wing length, culmen length, gap length, the third primary feather (abbreviated as ‘P3’ below) and length of tarsus and claw) of nestlings were larger than 0.9 (P < 0.01, Table 2), indicating that body parameters could be replaced each other at some extent; 6) The most important functions of the nestling organ developed preferentially (Table 3), in accordance with the energy allocation hypothesis. In summary, Yellow-bellied Prinia had relatively higher feeding frequencies and k values, possibly due to rich food source in our study area, and/or an adaption to highly variable nest habitats.