Strong enhancement of exchange bias (EB) effect in phase-separated CaMn 0.9Ru 0.1O 3 manganite with ferromagnetic phase heavily suppressed under pressure was observed in the measurements of field-cooled magnetization hysteresis loop. It was found that both EB field H E and normalized remanence asymmetry pronouncedly increase with increasing pressure P, enlarging by one order of magnitude at P = 10 kbar. In contrast, the coercive field H C shows a non-monotonic variation with pressure, reaching a maximum value at around 5 kbar. Such unusual H C(P) dependence may be explained by transformation from multi-domain to single-domain state in a system of ferromagnetic (FM) size-variable particles. Comparison of H E(P) with H C(P) data indicates remarkable enhancement of EB with decrease in H C in the pressure range between 5 and 10 kbar. It is argued that a strong increase of H E under pressure is attributed to the suppression of FM phase, i.e., to the decrease in size of FM clusters embedded in antiferromagnetic matrix. Presented results show that the EB effect can be tuned in a wide range by external pressure.