addressing probabilistic, and unstructured problems, thus is anticipated to solve the von Neumann bottleneck and become the mainstay of contemporary computing systems. [1,2] Synapses serve a crucial function in signal transmission in the biological neural system. [3] They transmit signals through neurotransmitters in a manner similar to that of field-effect transistors, where source-drain current changing in response to changes in gate voltage. In addition, organic materials are solutionprocessable, [4][5][6][7] thus simulating the functions of biological synapses by organic field-effect transistors has received intensive attention. [8,9] Most recently, higher performance requirements for devices are put forward to support practical applications, including fast switching speed, low energy consumption, low operating voltage, and strong compatibility with flexible substrate. Traditional planar field effect transistors struggle to accomplish these functions. Conversely, vertical organic field-effect transistors (VOFETs) have a more stable sourcedrain current and a changeable channel length that depends Organic field-effect transistors with parallel transmission and learning functions are of interest in the development of brain-inspired neuromorphic computing. However, the poor performance and high power consumption are the two main issues limiting their practical applications. Herein, an ultralowpower vertical transistor is demonstrated based on transition-metal carbides/ nitrides (MXene) and organic single crystal. The transistor exhibits a high J ON of 16.6 mA cm −2 and a high J ON /J OFF ratio of 9.12 × 10 5 under an ultralow working voltage of −1 mV. Furthermore, it can successfully simulate the functions of biological synapse under electrical modulation along with consuming only 8.7 aJ of power per spike. It also permits multilevel information decoding modes with a significant gap between the readable time of professionals and nonprofessionals, producing a high signal-to-noise ratio up to 114.15 dB. This work encourages the use of vertical transistors and organic single crystal in decoding information and advances the development of low-power neuromorphic systems.