It is well known that during evolution three types of respiratory proteins that can bind oxygen reversibly appeared. These are globins (myoglobin, haemoglobin and chlorocruorin), haemocyanin and haemerythrin. Most globins are composed of 140-160 amino acids. The amino acid sequence homology between globins belongs to distantly related organisms is low, but they have a very similar three-dimensional structure - the so-called myoglobin fold (Bolognesi et al., 1997). Myoglobin is a haemoprotein contributing to intracellular oxygen storage and transcellular facilitated diffusion of oxygen (Wittenberg, 1970). In contrast to monomeric vertebrate myoglobins, some gastropod myoglobins exist as dimers. Among invertebrates, molluscs has provide important evidences to globins study, a amino acid sequence derived of cDNA shows that gastropod Suculus diversicolor’ s myoglobin is homolog with human indoleamine dioxygenase (IDO). This find indicates a alternative way for myoglobin evolution. This work has proposed to study some biochemistry, molecular and structural aspects of the Biomphalaria myoglobins to contribute for knowledge about the funtion and evolution of this proteins. We discovered that myoglobins of Biomphalaria straminea and B. tenagophila are coded by nucleotide sequences with 456 base pairs; these sequences are very similar between them. These sequences (cDNA) were constructed and caracterized from mRNA using specific primers and bioinformatic tools. Native myoglobins of both Biomphalaria straminea and B. tenagophila were purified from buccal mass, where these proteins are more concentrated, and they were analysed by SDS-PAGE and mass espectrometry. Molecular mass, about 16 kDa, is in agreement with cDNA data and confirm the monomeric nature of these globins. In accordance with three-dimensional structure models obtained by mollecular modeling, the myoglobins of Biomphalaria straminea, B. glabrata and B. tenagophila presents the classic myoglobin fold. Primary sequences and three-dimensional structure assessement showed the presence of conserved residues that characterize the globin signature, and it showed that the strutural models have coherence.