We report on electron beam manipulation and simultaneous transmission electron microscopy imaging of gold nanoparticle movements in an environmental cell. Nanoparticles are trapped with the beam and move dynamically toward the location with higher electron density. Their global movements follow the beam positions. Analysis on the trajectories of nanoparticle movements inside the beam reveals a trapping force in the piconewton range at the electron density gradient of 10(3)-10(4) (e·nm(-2)·s(-1))·nm(-1). Multiple nanoparticles can also be trapped with the beam. By rapidly converging the beam, we further can "collect" nanoparticles on the membrane surface and assemble them into a cluster.