The study investigated the growth response of looseleaf lettuce (Lactuca sativa Linn.) applied with bio-organic fertilizer (BOF) consisting of rabbit manure and Trichoderma spp. produced under aerobic conditions. Composting process was done within 60 days. Complete randomized design was used for 5 treatments based on the volume of BOF applied. BOF material was analyzed for its total NPK, pH, moisture content, organic matter, total organic carbon, and C:N ratio. Through fertilizer analysis, the total N of the BOF material was found to be 0.94%, total P was 1.87%, and total K was 0.20%. When BOF was applied to the lettuce seedlings in different levels, T4 provided the optimal growth for final plant height (26.248±0.81 cm, p<0.05), total number of leaves (8.20±0.15 cm, p<0.05), longest leaf (19.93±0.15 cm, p<0.05), width of longest leaf (13.88±0.15 cm, p<0.05) and leaf diameter (51.38±0.21 cm, p<0.05) compared with plants dressed with inorganic fertilizer. The treatment with applied BOF obtained a significant total leaf yield per pot with T4 (1532.50±1.75 g, p<0.05) having the highest yield. Based on the findings of the present study, the high growth response of lettuce may be attributed to the potential synergistic relationship between Trichoderma spp. and rabbit manure. Furthermore, the results support the effectiveness of Trichoderma spp. in enhancing the soil’s macronutrient profile post-application.