With the rapid evolution of technologies and markets in the IT industry, it is especially crucial for small and medium-sized enterprises (SMEs) in the IT sector to possess the dynamic capability of seizing opportunities. This paper adopts the concept of “opportunity–seizing capability (OSC)” from the perspective of dynamic capability, and investigates its impact on relative firm performance via new market development. Furthermore, we examine whether environmental uncertainty influences the effect of a firm's OSC. Our hierarchical ordinary least squares regression results obtained using the data of 215 IT SMEs indicate that new market development is an important link between a firm's OSC and relative performance. The positive effect of a firm's OSC on new market development is stronger under a highly uncertain business environment. The findings indicate that enhancing an IT SME's OSC is crucial for its survival, particularly under an uncertain business environment.