Function inlining schemes are used to reduce the execution time of a program, but function inlining usually increases the code space due to the use of inlined functions. There are extreme limitations of memory space and battery capacity in embedded systems such as wireless sensor nodes. Function inlining should be performed selectively. If we reduce the execution time of a program by means of function inlining, we can reduce the amount of energy that is consumed. Therefore, function inlining is useful in resource-constrained embedded systems. Basic function inlining schemes were proposed in the previous studies. However, these schemes were too coarse-grained, and did not analyze the impact of function inlining on resource-constrained embedded systems. In this paper, we propose a fine-grained function inlining scheme which considers the execution rate of the individual functions. We also present an analysis of the impact of function inlining schemes on resource-constrained embedded systems, in terms of energy consumption and code memory usage. Based on experimental results, we show that the proposed fine-grained function inlining scheme can improve the level of energy efficiency.