The marine microalga Chroomonassp. isolated from Venezuela was grown in semicontinuous culture in order to study the effect of renewal rate and nutrient concentration on alloxanthin, chlorophyll a, carotenoid, carbohydrate, exopolysaccharide, protein and cell productivity. Maximal cell productivity of 8.43 ± 1.8 and 8.81 ± 2.3 × 109cell l−1day−1were achieved with renewal rates of 30 and 40%. Maximal protein and chlorophyll productivity of 64.64 ± 2.3 and 2.72 ± 0.3 mg l−1day−1were obtained with renewal rate of 20 and 30%. Biochemical composition of Chroomonassp. was influenced by renewal rate. Nutrient concentration seems not to affect cell, protein, chlorophyll and carotenoid productivity. However, carbohydrate and exopolysaccharide productivity of 7.56 ± 0.4 and 9.57 ± 1.2 mg l−1day−1were increased at 12 mM NaNO3(P< 0.05). Also, alloxanthin and chlorophyll aproduction analysed by HPLC, were higher between 8 and 12 mM NaNO3at a renewal rate of 30%. Results demonstrated that a renewal rate of 30% and nutrient concentration at 8 mM NaNO3optimize the cell, protein, carbohydrate, chlorophyll a, and exopolysaccharide productivity in semicontinuous cultures of Chroomonas. This microalga, as biological source of commercially valuable compounds, shows high capacity for changing its productivity and biochemical composition in semicontinuous system on the basis of nutrient concentration and the renewal rate.