Macrophages are white blood cells of the innate immune system that play disparate roles in homeostasis and immune responses. As a result, they have the capability to alter their phenotypes to pro-inflammatory (M1) or anti-inflammatory (M2) subtypes in response to their environment. 8-15% of the macrophage transcriptome has circadian oscillations, including genes closely related to their functioning. As circadian rhythms are also associated with cellular phenotypes, we hypothesized that the polarization of macrophages to opposing subtypes might differently affect their circadian rhythms. We tested this by tracking the circadian rhythms of the mouse model macrophage cell line, RAW 264.7, which was stably transfected with Bmal1:luc and Per2:luc reporters, representing a positive and a negative component of the core molecular clock. The strength of rhythmicity was assessed using three measures: the relative power of the circadian band in the power spectral density, the rhythmicity index computed as the height of the third peak of the correlogram, and the maximum value of the chi square periodorgram. The period and amplitudes of the de-trended, smoothed time-series were estimated both by fitting to a damped cosine curve and by identifying the peak and trough of each cycle. M1 polarization decreased amplitudes and rhythmicities of both Bmal1:luc and Per2:luc, but did not significantly affect periods, while M2 polarization increased periods and caused no substantial alterations to amplitudes or rhythmicity. As macrophage phenotypes are also altered in the presence of cancer cells, we then tested the circadian effects of conditioned media from two mouse breast cancer cell lines on macrophage circadian rhythms. Media from highly agressive 4T1 cells caused loss of rhythmicity, while media from less aggressive EMT6 cells yielded no changes. As macrophages are known to play roles in tumors, and oncogenic features are associated with circadian rhythms, we also tested whether conditioned media from macrophages can alter circadian rhythms of cancer cells. We found that conditioned media from RAW 264.7 cells resulted in lower circadian rhythmicities and periods, but higher circadian amplitudes in human osteosarcoma, U2OS-Per2:luc cells. Taken together, our study shows that different circadian characteristics exist based on macrophage phenotypes, and suggests further that there is an association between circadian rhythms and macrophage polarization state. Additionally, our data shows that macrophages treated with breast cancer-conditioned media have circadian phenotypes similar to those of the M1 subtype, and cancer cells treated with macrophage-conditioned media have circadian alterations, providing insight to another level of cross-talk between macrophages and cancer cells that merits further investigation.