Size-dependent vibrational and instability behavior of fluid-conveying magneto-electro-elastic (MEE) tubular nano-beam subjected to magneto-electric potential and thermal field has been analyzed in this study. Considering the fluid-conveying nanotube as an Euler-Bernoulli beam, fluid-structure interaction (FSI) equations are derived by using non-classical constitutive relations for MEE materials, Maxwell's equation, and Hamilton's principle. Thereafter, taking the non-uniformity of the flow velocity profile and slip boundary conditions into consideration, modified FSI equation is obtained. By utilizing Galerkin weighted-residual solution method, the obtained FSI equation is approximately solved to investigate eigen-frequencies and consequently instability (critical fluid velocity) of the system. In numerical results, a detailed investigation is conducted to elucidate the influences of nano-flow and nano-structure small scale effect, non-uniformity, temperature change, and external magneto-electric potential on the vibrational characteristics and stability of the system. This work and the obtained results may be useful to smart control of nano structures and improve their efficiency.