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　ultralow-power　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　x　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.