The present study was conducted to compare the effect of follicle size and clinical examination on non-return rate (NRR) and to investigate whether the oestrus signs or ovulatory follicle sizes (OFS) have positive effect on pregnancy success of cows in field conditions alternatively. The clinical findings of oestrus in animals were examined by visual observation and some clinical tests undergoing spontaneous oestrous cycles and then, all cows were artificially inseminated (AI) by frozen-thawing semen. The overall mean value of NRR was obtained as 67.08 % in all cows, and also the NRR was affected by size of the ovulatory follicle (P<0.05), vulva edema, vaginal hyperemia and ferning of the cervical mucus (P<0.01). The highest rate of non-return (92.0 %) was achieved with inseminated range of 15.0-17.99 mm ovulatory follicle sized cows. However significantly (P<0.01) high NRR (84.78 %) was observed to increase the ferning of cervical mucus. The ovulatory follicle was located more often (P<0.01) on the right (64.10 %) than the left (35.90 %) ovary, but there was no effect of location of the ovulatory follicle on the NRR. In conclussion, NRR was greater spontaneously oestrous signed and inseminated cows of which vulva edema, vaginal hyperemia and ferning of cervical mucus were high and OFS was moderate. Therefore, the exhibiting behavioral oestrus can be evaluated with ovulatory follicle size and ferning of cervical mucus, the fertility may be improved.