The application of conventional lateral flow immunoassay (LFIA) remains challenging due to its single signal readout and poor sensitivity. In this work, we developed J-aggregated fluorescence nanoparticles (JNPs) with multichromatic performance and employed them as reporters for the simultaneous and sensitive detection of T-2 and AFB1 toxins on the LFIA platform. Upon the strong confinement effect of nanoparticles, the emission region of JNPs was red-shifted from ∼545 to ∼620 nm, exhibiting a strong J-aggregation phenomenon. Subsequently, two JNPs with green emission and red emission were employed for the development of multiplexed LFIA platform (JNPs-LFIA) for on-site quantitative detection of T-2 and AFB1 toxins, with the limits of detection of 0.645 ng mL-1 and 0.0035 ng mL-1, which were 3.5-fold and 12.2-fold lower than those of AuNPs-LFIA, respectively. Overall, this work provides an efficient strategy for the design of multichromatic immunoprobes and promotes the development of reporters in biosensing application.