Large animals, having large vocal organs, produce low sound frequencies more efficiently. Accordingly, the frequency of vocalizations is often negatively related to body size across species, and also among individuals of many species, including several non-oscine birds (non-songbirds). Little is known about whether song frequency reveals information about body size within oscine species, which are characterized by song learning and large repertoires. We asked whether song frequency is related to body size in two oscines that differ in repertoire size: the dark-eyed junco (Junco hyemalis) and the serin (Serinus serinus). We also asked whether the extent to which receivers sample repertoires might influence the reliability of their assessment of body size. We found that none of the frequency traits of song that we investigated was related to male body size, nor did more extensive sampling of repertoires lead to any relationship between frequency and body size. Possible reasons for these results are the small range of variation in size within species, or the elaborate vocal physiology of oscines that gives them great control over a wide frequency range. We discuss these results as they relate to female preferences for high-frequency song that have been previously reported for oscine species.