The aims of this study were to investigate (1) the efficacy of chitosan in 2 forms, the monomer N-acetyl glucosamine (NAG) and a chloride salt of chitosan (MIX) in culture systems HCT-8 and Caco-2 cell lines in vitro for Cryptosporidium parvum compared with a positive control, paromomycin (PARO) a classical drug used in veterinary medicine; (2) the action of a chitosan-yeast-bacteria based product on neonatal diarrhea and mortality in goat kids. Cryptosporidiosis is considered as an economically important disease with clinical signs and death in young ruminants. The usual clinical symptom is acute diarrhea affecting animals from 1 to 3 weeks old. As no drugs are fully effective in the treatment of cryptosporidiosis in man and animals, the research for new therapeutic agents is crucial. Chitosan is a sugar that is obtained from the hard outer skeleton of shellfish, including crab and shrimp and it is used in medicine. It has been found to be active against a variety of diseases including antimicrobial and anti-tumoral effects. Immunofluorescence technique was used for the identification and enumeration of the parasites. The results showed a significant reduction of viability of Cryptosporidium oocysts (>95%) after pre-incubation of 24h at 37°C with PARO (P < 0.001), MIX and NAG (P < 0.001). Additionally, PARO, MIX and NAG inhibited significantly the development of C. parvum in HCT-8 and Caco-2 cell lines (P < 0.005). These effects were dose-dependent. Synergistic effects were obtained when NAG treatment was associated with Paromomycin. The efficacy of MIX in combination with yeast and bacteria (Optisaf FIRST, Phileo, France) was evaluated experimentally in goat neonates inoculated with C. parvum oocystes (10⁶ oocytes/mL) per oral route. Preliminary results showed a significant reduction in oocyst shedding and diarrhea score in goat kids and mortality was significantly reduced (36%) in treated animals (P < 0.05) compared with the control group (90%). In conclusion, these findings provide evidence of in vitro inhibitory activities of chitosan against C. parvum and its combination with yeast-based products revealed promising in lessening the incidence of neonatal diarrhea in young ruminants.