This study employs financial data of Korean accounting firms for the sample period from 1997 to 2012 and analyzes the behavior of accounting firms' operating expense and its determinants. Empirical analysis of pooled data for accounting firms reports that operating expense exhibits stickiness with respect to operating revenue which is assumed to a single cost driver. Further analysis reveals that the degree of stickiness for operating expense is lower in revenue-declining periods that were preceded by revenue-declining period, while operating expense is stickier at firms that require relatively more employees to support their operating revenue. Futhermore, classifying accounting firms into three groups: Big N affiliated incumbent firms (BIG), incumbent firms that are not affiliated with Big N (OLD), and newly established firms since 1997 (NEW), I empirically observe stickiness for operating expense only in NEW, not in BIG or OLD. Breaking down operating expense further into labor-related expense and other expenses, I find that labor-related expense shows strong stickiness, while other expenses do not. This result suggest that stickiness of operating expense is driven mainly by labor-related expense, not by other expenses.