The widespread inulin use in food industry is based on their technological and nutritional properties. This study analyzed pH, titratable acidity (TA), lactose and lactic acid in prebiotic sheep milk yogurt (PSMY), with different inulin content (0, 2, 4 and 6%) immediately after incubation and during 28 storage days at 4 ± 2°C. The bacteriological count was performed at the 1st and 28th days of storage. On the 1st day, Streptococcus thermophilus counts were: 9 log, 10 log, 11 log, 11 log cfu.mL⁻¹, whereas Lactobacillus delbrueckii subs. bulgaricus were 8 log, 8 log, 8 log, 9 log cfu.mL⁻¹. On the 28th day, S. thermophilus were 8 log, 8 log, 8 log, 9 log cfu.mL⁻¹, and L. bulgaricus were 6 log, 7 log, 7 log, 7 log cfu.mL⁻¹ for PSMY treatments, respectively. There was a significant decrease (P < 0.05) in both lactic acid bacteria during storage, due to inulin protective effect. As expected, the pH decreased and TA increased significantly (pH and TA: r = −0,835; P < 0.05) of PSMY during storage. There was a significant difference (P < 0.05) between PSMY with different inulin content, being 0% the most acidic and 6% the less acidic. As well, pH values were not significantly influenced (P < 0.05) by the inulin addition. Lactose had a significant decrease (P < 0.05) expected through storage (r = −0.759) in PSMY. Inulin content had a significant impact (P < 0.05) in lactose concentration, because lactose amount was higher in PSMY 6%, dropping in each treatment until PSMY 0%, which had a significantly lower concentration (P < 0.05) of lactose during measurement days. This statement suggested that the acid lactic bacteria consumed inulin instead of lactose proportionally with inulin amounts, meaning that lactose was proportionally degraded by lactic acid bacteria into lactic acid (lactose and lactic acid: r = −0.826). Thus, lactic acid concentration of PSMY 0% was higher (P < 0.05) compared with others. Lactic acid had a significant increase during storage (r = +0.936; P < 0.05) in PSMY. Moreover, inulin amount delayed the acidity increase in PSMY (lactic acid and TA: r = +0,919), suggesting that inulin fiber retarded the acidity growth in yogurts, which is pleasant for consumer and dairy industry.