Research was designed to obtain a selective bottom part of jodang trap on shell length of Babylon snails (Babylonia spirata). A line of grids was used to form bottom part construction of trap with gap wide of 2.4 cm. Construction is called selective if it can be passed by shells with length of p < 4.27 cm. According to Firdaus (2002), Babylon snails have done spawning at shell length of 4.27 cm. Puspito (2009) found those shells have circular diameter of shell cross-section of 2.4 cm. Furthermore, 54 traps were operated in Palabuhanratu waters. From the research, traps was quite selective to catch Babylon snails with length of shell p ≥ 4.32 cm. Babylon snails with shell length of 4.27 cm ≤ p < 4,32 cm could stil passed trough the traps.