Paclitaxel (PTX), methotrexate (MTX), and 5-fluorouracil (5-FU) are commonly-used small molecule anti-tumor drugs for breast cancer. Unfortunately, drug resistance occurs with long-term treatment or excessive use, and the high concentrations of PTX, MTX, and 5-FU in patients may lead to side effects with dose-limiting toxicities, such as myelosuppression, hepatotoxicity, and peripheral neuropathy. Therefore, concentration monitoring of PTX, MTX, and 5-FU in clinical treatment is very important. We prepared highly sensitive and specific monoclonal antibodies using several haptens, and established a multiple paper-based sensor utilizing optical signals of gold nanoparticles, which simultaneously detected PTX, MTX, and 5-FU in human plasma or urine with 10 min. A portable scanner for quantitative detection in plasma and urine samples was used, and the calculated limit of detection (cLOD) values were 0.002 and 0.142 μg/mL for PTX, 0.187 and 0.976 ng/mL for MTX, and 0.057 and 0.128 μg/mL for 5-FU, respectively. In the recovery test, the recovery rates and the coefficient of variation were 85.84%–108.81% and 1.23%–8.80%, respectively, indicating the reliability and accuracy of the multiple gold immunochromatographic strip (GIS). In addition, for the determination of collected clinical plasma samples, the correlation between the test data of the multiple GIS and liquid chromatography–tandem mass spectrometry (LC–MS/MS) was good. Therefore, the developed multiple GIS could be applied to the rapid detection of PTX, MTX, and 5-FU in different clinical samples.