Carboxylation efficiency in fully expanded leaves of strawberry (Fragaria ${ imes}$ ananassa cv. Maehyang) was estimated based on net $CO_2$ assimilation rate ($A_n$) as a function of chloroplastic $CO_2$ concentration ($C_c$). To estimate the mesophyll conductance ($g_m$) and then construct $A_n-C_c$ curves, $A_n$ and electron transport rate as a function of intercellular $CO_2$ concentration ($C_i$) were simultaneously determined at a range of 50 to $2,200{mu}mol;CO_2/mol$ air at a saturating photosynthetic photon flux (PPF), $1,200{mu}mol{cdot}m^{-2}{cdot}s^{-1}$. Mitochondrial respiration rate ($R_d$) and $CO_2$ compensation point in the absence of $R_d$ required for calculating $g_m$ were found to be $0.15{mu}mol{cdot}m^{-2}{cdot}s^{-1}$ and $44.1{mu}mol;CO_2/mol$ air, respectively, as determined from $A_n-C_i$ curves below $200{mu}mol;CO_2/mol$ air at three different PPFs. Both stomatal conductance ($g_s$) and $g_m$ decreased with increasing $C_i$. However, the gm responded more sensitively to various $C_i$ than the $g_s$. The gm was significantly lower than the $g_s$ at $C_i$ beyond $600{mu}mol{cdot}mol^{-1}$ air examined. Maximum carboxylation efficiency (${alpha}_{cmax}$) derived from $A_n-C_c$ curves was $0.28{mu}mol{cdot}m^{-2}{cdot}s^{-1}$ and 2.2 times higher than that from $A_n-C_i$ curve. Since the $A_n-C_i$ curve was based on infinite $g_m$, the ${alpha}_{cmax}$ derived from the $A_n-C_i$ curve might be underestimated. Actually, $g_m$ was rather dynamic with changing $C_i$ and thus a crucial component of the diffusional limitation of $A_n$. For estimating photosynthetic characteristics in strawberry leaves more accurately, $A_n-C_c$ curve should be constructed in consideration of $g_m$, especially for closed plant production systems.