We present two new records for the vulnerable dwarf marmoset, Callibella humilis. The first record, based on observed and photographed individuals, is from a campinarana area on the left (west) bank of the Rio Madeirinha, a left (west)-bank tributary of the Rio Roosevelt in the state of Amazonas, municipality of Novo Aripuanã and extends the distribution of the species ~270 km southwards, to the left (west) bank of the rio Roosevelt. The second record is based on an individual collected from the mouth of the Rio Roosevelt, at less than 10 km from the type locality of Mico marcai. This indicates that the species occurs sympatrically with M. marcai and probably Mico melanurus. We also present the first sonogram analysis of its long call structure, which shows some similarities, in the note duration and frequency, with Cebuella pygmaea and Mico argentatus.