Homalopteroides avii, new species, is described from the Rajang River basin, Sarawak, Malaysian Borneo. It is distinguished from all other species of Homalopteroides by a wider gape of 28.5–33.3% HL vs. 22.3–24.2% for H. wassinkii, 20.0–28.4% for H. modestus, 19.1% for H. rupicola, 19.1–27.3% for H. smithi, 20.0–23.2% for H. stephensoni, 20.2–26.9% for H. weberi, 18.4–26.0% for H. tweediei, 17.3% for H. indochinensis, 17.4–21.2% for H. nebulosus, and 18.0–19.0% for H. yuwonoi. It is further distinguished from species of Homalopteroides by the presence of a lateral cephalic stripe vs. absence in H. modestus, H. rupicola, H. smithi, H. tweediei, H. nebulosus, and H. yuwonoi; deeper caudal peduncle, 10.1–10.9% SL, vs. 8.4–9.0% for H. wassinkii, 8.7% for H. rupicola, 7.7–9.1% for H. smithi, 6.1–6.6% for H. stephensoni, 6.7–8.0% for H. weberi, 8.0–9.4% for H. tweediei, 9.3–9.8% for H. nebulosus, 8.7% for H. indochinensis, and 7.3% for H. yuwonoi; circumpeduncular scale count of 20–22 vs. 16 for H. rupicola, H. stephensoni, H. nebulosus, H. indochinensis, and H. yuwonoi, 14–16 for H. tweedei, and 16–18 for H. smithi and H. weberi; total pelvic-fin ray count of 9 vs. 10 for H. stephensoni, H. weberi, and H. yuwonoi. The species is relatively large for the genus, reaching 52.9 mm SL.