Tribulus terrestris is believed to affect the biological functions of fish. Its effects may differ based on the dosage, which has yet to be established for Clarias gariepinus. This study aimed to identify the lethal (LC50) and the non-lethal concentration of ethanol extract from Tribulus terrestris on fry of catfish (Clarias gariepinus). A 96-hour acute toxicity assessment of the ethanol extract was conducted using Probit analysis. The non-lethal concentration of the ethanol extract of Tribulus terrestris was determined based on the LC16, LC50, and LC84 values derived from the response curves for exposure durations of 6, 12, 24, and 48 hours (Figure 1). The LC50 values were recorded as 9.34 mg/L, 5.95 mg/L, 5.43 mg/L, 3.16 mg/L, 3.16 mg/L, and 3.16 mg/L for the exposure durations of 6, 12, 24, 48, 72, and 96 hours, respectively (Table 1). A non-lethal concentration of 1.4 mg/L was established from the LC16, LC50, and LC84 data (Figure 1). These findings suggest that as Clarias gariepinus are exposed to the ethanol extract of Tribulus terrestris for an extended duration, a smaller concentration of the extract is sufficient to lethally affect 50% of the population. Therefore, concentrations of 1.4 mg/L or less of the ethanol extract of Tribulus terrestris are considered non-lethal to catfish Clarias gariepinus.