F0 variations of tone languages are not only constrained by individual lexical tones but also affected by various contextual factors. In this work the effects of two factors, i.e. tonal context and focal emphasis, on F0 contours of Cantonese are investigated by a controlled experiment. All the four combinations of carryover/anticipatory and assimilatory/dissimilatory effects by adjacent tones are observed, with different magnitudes and domains. The effect of focus is not local but shows a similar nature in pre-focus, on-focus, and post-focus domains, with both raised F0 values and expanded F0 ranges. The interactions between the two factors are also analyzed.