This work characterizes the adsorption of aflatoxin B (AFB), ochratoxin A (OTA), and zearalenone (ZEN) by dry micronized olive pomace (OliPom) and grape stems (GrapStem). Their performance was compared with that of three other materials, activated carbon (ActCarb), bentonite (Bent), and a commercial product (ComProd). Experiments were conducted in vitro at several pH values using buffer solutions. For OTA and ZEA, the strongest adsorbent was ActCarb, with 5 mg/mL being sufficient to bind > 99% of all the mycotoxins. For AFB, ComProd and Bent were the most effective adsorbents, as 0.5 mg/mL bound > 95% of this mycotoxin. Among the two agro by-products, GrapStem was the strongest binder, with 10 mg/mL being sufficient to bind at least 90% of all the mycotoxins (except OTA at pH 7). OliPom was the least efficient material, but at a concentration of 30 mg/mL, its performance was similar to GrapStem. Adsorption isotherms were calculated, and ActCarb showed the maximum adsorption capacity (Q), with values that ranged from 19 to 24 μg/mg for pH 2 and from 17 to 20 μg/mg for pH 7. ComProd, Bent, and GrapStem showed more similar Q between them (1.4-4.4 μg/mg for pH 2 and 0.5-4.8 μg/mg for pH 7).