Negative energy balance (NEB) caused by high milk yield and insufficient feed intake in early lactation has been related to compromised cow health and fertility. Recent studies show that the NEB in early lactation could be alleviated by omitting or shortening dry period in dairy cows. It can therefore be hypothesized that omitting or shortening dry period improves fertility in dairy cows. The objective of this study was to evaluate the effects of dry period length on onset of ovarian activity and ovarian cyclicity in Holstein-Friesian dairy cows within 100 d in milk (DIM). The cows (60 primiparous and 108 multiparous) were randomly assigned to one of 3 dry period lengths (0, 30, and 60 d). Milk samples were collected 3 times a week for progesterone concentration analysis until 100 DIM after calving. Onset of luteal activity (OLA) was defined as the occurrence of at least 2 succeeding milk samples with progesterone concentrations ≥2 ng/mL. Normal resumption of ovarian cyclicity was defined as onset of first luteal activity occurring within 45 DIM, and followed by regular ovarian cycles of 18 to 24 d in length. Data are expressed as percentage or LSMEANS ± SEM. Within 100 DIM postpartum, cows with a 0-d dry period had greater incidence of normal resumption of ovarian cyclicity compared with cows with a 60-d dry period (53.2% vs. 26.0%; P = 0.01). Cows with a 30-d dry period tended to have greater incidence of normal resumption of ovarian cyclicity compared with cows with a 60-d dry period (47.7% vs. 26.0%; P = 0.09). In addition, cows with a 0-d dry period tended to have shorter interval from calving to first commencement of luteal activity (23.1 vs. 28.9 ± 2.0 d; P = 0.07) compared with cows with a 60-d dry period. Overall, our results demonstrate that omitting dry period improves resumption of ovarian cyclicity within 100 DIM in the subsequent lactation.