布朗马达是奈米或分子设备，以热趋动进程(化学应用)来控制及用来产生指向性的运动及做机械能或电能的功。这个小马达在粘性远大于惯性的环境下运用，而且热杂讯使得它有如在龙卷风中行走般地难以走在一定的方向上：推动马达于一指定方向的力比环境所施的无规则的力要小的许多。因为这一类的马达强烈地依赖着热杂讯，使得布朗马达只在奈米尺度下才可能实现。

在生物学里，许多细胞内的蛋白质分子马达实际上即是一种布朗马达。此一分子马达将存在三磷酸腺苷内的化学能转换至机械能。例如三磷酸腺苷酶马达，其作用即是水解ATP来产生指向性的能量。此一指向性的能量会使粒子(或离子或多肽)偏向；其结果最终会使得粒子扩散的静移动会强烈地偏向一个方向。

Brownian motors are nano-scale or molecular devices by which thermally activated processes (chemical reactions) are controlled and used to generate directed motion in space and to do mechanical or electrical work. These tiny engines operate in an environment where viscosity dominates inertia, and where thermal noise makes moving in a specific direction as difficult as walking in a hurricane: the forces impelling these motors in the desired direction are minuscule in comparison with the random forces exerted by the environment. Because this type of motor is so strongly dependent on random thermal noise, Brownian motors are feasible only at the nanometer scale.