Identifying individual behavioural characteristics associated with physiological indicators is useful for animal production and welfare to provide appropriate management in stressful situations. The present study examined relationships between milk productivity and milk cortisol concentration (MC) with behavioural characteristics of newly calved cows when introduction into a new social group. Behaviour of 37 newly calved cows were observed twice during one week after their introduction to a production group (approximately 4 hours/day around morning milking). Milk samples for MC measurement and milk trait data were collected on the test day every two months until drying-off. Mean MC was 35.4ng/dl. Estimated total, inter-cow and inter-test day variances of MC were 1266.0, 50.6, and 41.8, respectively. Each behaviour and milk trait was subjected to linear mix model analysis with a random effect of cows, for estimating the individual best linear unbiased prediction (BLUP) of each trait. Then behavioural BLUP data were subjected to principal component (PC) analysis. Three PCs with eigenvalues greater than 1.0 explained 63% of the total variation. The first PC, with large loadings for eating and allogrooming, was positively correlated with BLUP of milk yield (r=0.41, p<0.05). The first PC showed a significant relation with milk productivity. However, the second PC, with large loadings for drinking and self-grooming, was uncorrelated with milk traits, but had a negative correlation with BLUP of MC (r=-0.32, p<0.05). The third PC, with large loadings for exploring, fighting and the frequency of agonistic behaviour, was uncorrelated with all traits. Results show that MC might be an indicator of certain behavioural characteristics which were independent of productivity.