Recent evidence has shown that large-conductance calcium-activated potassium (BKCa) channels are involved in mediating uterine relaxation. The objective of this study was to determine the localisation and protein expression of the α subunit of BKCa channels in the myometrium of term pregnant women with and without labour. Myometrial biopsies obtained from singleton term pregnant women undergoing either (1) elective caesarean section (n = 26) or (2) emergency caesarean section after spontaneous labour (n = 25) were used for immunohistochemistry, immunofluorescence and Western blotting. Anti-α BKCa channel monoclonal antibody was used to localise and quantify BKCa channel protein. Myometrial BKCa channel levels were normalised to rat brain which was used as an internal standard. Data were presented as mean ± SEM. Differences between groups were analysed by two-tailed unpaired t-test. A P value < 0.05 was considered to be statistically significant. Immunohistochemistry and immunofluorescence revealed positive staining at the plasma membrane and in the cytosol of the myometrial cells with similar intensity between both groups of women. Western blotting demonstrated a 125 kDa band corresponding to the α subunit of the BKCa channel. The protein expression of the α subunit BKCa channel in myometrium was significantly higher in pregnant women without labour (32.9 ± 3.4%) than those with labour (20.3 ± 3.4%; P < 0.05).