Camelina meal and camelina expeller could become an alternative to currently available sources of protein due to their great protein content. The objective of this study was to compare the effect of camelina meal and camelina expeller on rumen fermentation and nutrient flow in an in vitro system. Treatments were 4 diets in which the main protein sources were: soybean meal-44 (SM), 00-rapeseed meal (RM), camelina meal (CM) and camelina expeller (CE) at 12.7%, 16.6%, 16.9% and 18.1% of inclusion (DM basis), respectively. Diets were formulated with a 90:10 concentrate:forage ratio, and to be isocaloric (2.8 Mcal ME/kg DM) and isonitrogenous (13.5% CP, on DM basis). Eight 1,320-mL dual-flow continuous culture fermentors were used in 2 replicated periods with 5 d for adaptation and 3 d for sampling. Temperature (39°C), pH (6.2), and liquid (0.10/h) and solid (0.05/h) dilution rates were maintained constant. Diets (95 g DM/d) were fed in 3 equal portions during the day. Effluent samples were collected from a composite of the 3 sampling days, and bacteria were isolated from fermentor flasks on the last day of each period. A randomized block design was used. Differences were analyzed using the MIXED procedure of SAS. The model contained treatment as fixed effect and period as random effect. The CE diet tended to present a higher (P < 0.06) OM true digestibility (57.4%) than SM (48.0%). Total VFA was higher (P < 0.009) in CE and CM than in SM (138.8 mM and 135.6 mM vs 119.6 mM; respectively) and butyrate proportion was lower (P < 0.02) in CM than in SM (12.1 mol/100 mol vs 16.4 mol/100 mol; respectively). Dietary nitrogen flow tended (P < 0.06) to be lower in CE (1.13 g/d) than in CM (1.61 g/d) and CP degradation tended (P < 0.07) to be higher in CE than in CM. Although the efficiency of microbial protein synthesis was not affected by treatment, CE showed a higher digestibility than SM and higher CP degradation than CM, whereas CM showed similar results to the reference proteins (SM and RM) but increasing the total VFA concentration.